Sorry this a long post but I hope will help you.
Lulu was / is a very timid and wary cat. Your post reads very much like her, except instead of biting the vet Lulu shakes and is terrified. The first time we were both away for 3 days 2 nights my cat sitter who moves in barely saw her. She hid under our duvet and came out at night only. She even fed her the daytime meal at the base of our bed. 6 months ago we took on Kiki. She is a rescue so we didn't get a choice on personality. Kiki is a very outgoing kitten. In view of Lulu nervousness, we did intros slowly using a safe room and a travel dog kennel so they met at Lulu's pace. When we started letting them meet, Lulu would run off to another room for quite some time. But slowly she came around. In that time something happened and Lulu gained confidence. She doesn't hide for the whole time when new people come, she disappears with kiki at the start but they are back in 15 mins at most. She is still nervous for vet visits but so much better when they go together so we always tie in appointments at the same time when it's check ups etc. The biggest thing is they play together eat together, all except sleep together. But I am optimistic in time that may come.
So only from my experience I would say it can help just you need to be patient with intro and do it all at her pace. Oh and give her tons of love and affection through that intro process.

 

I think maybe exposing her to others repeatedly will help her become more social to humans. Is she too afraid to come out when strangers come into your home? If she's just wary and stays in the corner of your living room with a watchful eye, I'd buy a bag of treats and get her used to the exposure while instructing friends and family members to come and give her treats and proper way to pet (slow scratches to her chin area), to see if that helps her first. Or if your kitty just loves playtime, I'd invite others to play with her and see how she does before you go all out and adopt another kitty.

 

I have to disagree with that - I think even if she does allow contact with other people eventually it will not build her confidence the way a bond with another cat could. However, we all know that sometimes resident cats will not accept a new cat so that could be an issue. It could also be an issue since your cat is so strongly bonded to you and your husband and not to anyone else, she may really resent a newcomer competing for your affections. There are many variables and you would have to be prepared for many possible outcomes.

 

These are my first cats, so I don't know how to help this situation.

I do know that Book has gotten way more timid as he's aged. The only time it shows is when MowMow isn't there.

When he gets nervous he looks to MowMow. If MowMow is tense in a situation, Book really gets upset. Luckily, MowMow is a very confidant cat. He keeps Book (and I admit, me) calm and gives him confidence in scary situations. Imo an outgoing friend might help.

Not sure where Neelix fits in yet, he's a very friendly and confidant kitten, I hope he stays that way.

 

Ultimately we can give you our best guesses...but no one can be sure.

In my house Torri was a very confident kitten, but got sick at 1 year old and became very very anxious/nervous after that. With a lot of work she's been slowly coming around, but it's a very slow process. She'll be 7 in august and is only now (with a solid 3-4 years of effort put in) allowing people other than me and her Daddy to pet her...sometimes.

I'd suggest that you work with your girl first, and then consider a kitten in a few months depending on how the training goes.

IME the best things to help Torri come around were me not expecting too much, protecting her from feeling threatened, and managing her space.

Basically, if we have more than 2-3 people over (people I know and who know about how shy she is - so people I trust) I just put Torri away in her safe room. She doesn't want to deal with strangers, and it only stresses her out - so I give her a way out. The fewer negative experiences she has the easier it will be to teach her new people are fun.

For a long time I didn't allow anyone to touch her, I simple said she was really shy and uncomfortable with people other than myself and my SO. I had a few disgruntled friends, but a simple demonstration about having people in your personal space was enough to disuade them (I'd just move and stand uncomfortably close, then pat their head and ask "How comfortable are you right now?" - gets the point across admirably )

Once Torri knew I wasn't going to let anyone run over and grab at her (aka - that I'd keep her, and her space, safe) I would leave her out in the house with people I knew and trusted to follow directions. We'd ignore her and let her come over - or not - on her own time. If she came over I would give her a little treat. Once she got more comfortable I'd give my friend the treats and have them put the treats on the floor - offering a treat directly to her was still too threatening.

Because I took things so slowly Torri is now much more comfortable and will let certain friend of mine (generally calm and quiet people) pet her on a fairly regular basis, even coming over for pets! One or two strokes is still all she's comfortable with, but she IS comfortable with it. That's a huge step.

I also used clicker training to help build her confidence among my other cats.

IMO if you simply bring in a kitten it could go one of two ways; either it'll work out great - like in Jenny's case - or it'll go the complete opposite way and your girl will end up worse. Personally, it's not worth the risk. From someone who has worked with an anxious kitty for years, I wouldn't do anything to set her back.

 

Your girl may have come "from a nice family" but she missed out on some vital socialization skills as a kitten if she was taken from her momcat and siblings at 8 wks. Most of a cat's socialization happens in that month after eight weeks when the kittens are very rowdy and that's when they learn to control their claws and bite with each other, and to learn that people are generally friendly and kind and to be comfortable being picked up and petted by different people. I would accept her as she is, and she may mellow out as she gets older to strangers. Just yesterday I scratched the cheeks and petted a friend's cranky tortie and white girl. It's only lately that she's allowed "strangers" to do that and she just turned 13 yrs. As far as getting a kitten to help her to be more confident, imo her "nervous disposition" is likely genetic and doubt a kitten would make a difference with her. If she doesn't like adult cats, she probably won't like a kitten any better. It's possible you could foster a kitten to see how it would work out.

 

Your girl may have come "from a nice family" but she missed out on some vital socialization skills as a kitten if she was taken from her momcat and siblings at 8 wks. Most of a cat's socialization happens in that month after eight weeks when the kittens are very rowdy and that's when they learn to control their claws and bite with each other.

SUPER dittos!! What catloverami says is right on! Watching my foster kittens play has reinforced this lesson to me 1000 fold!! I will not let my kittens go before 12 weeks now if they are going to a home alone.

Some cats are just inclined to be nervous and skittish. I had the sweetest cat in Sicily named Annie. Before we could get her fixed she got pregnant and had 3 kittens. We kept the female thinking the apple does not fall far form the tree, right? WRONG! Little Maggie, who we loved and doted on since she was 2 days old was always nervous and a fraidy cat. That cat was NEVER right. :dis We think Annie must have mated with a feral cat and those genes were passed along.....if that is possible.

 

I wouldn't expect a kitten to give her confidence. It might but that would be an exception rather than a rule. Ask your vet about doing "happy visits" bring her absolute favorite treat. Something she rarely gets and give it to her at the vets only. Most vets will be happy to do this. A relaxed and happy cat is much easier to work with than a nervous cat. But she might not ever turn around. Some cats are just like that. It can be genetic.