Hello spirite and catloverami.
Although she appears to be quite healthy, Atari is still doing both the lip-licking and head-twitching after every meal without fail. She has not thrown up once since my last post, and she is both pooping and peeing like a champ. She is very active as well; tearing up her cardboard boxes, annihilating her toys and bolting through the house. Ever since we changed to her current diet, she went from a scared little kitty hiding underneath the couch, to a forceful presence in the room. Meowing and demanding attention, owning the room she is in. It's such a marvellous thing to see how something so small can change their entire being.
I had two vets looking at her during those visits, and I am inclined to put my trust in what they said. They both took their time to look her over even if nothing seemed wrong with her outside the vomitting. I like to believe that over time, I can tell a good vet from a lesser one. I had an unfortunate experience with my first kitty, Mioe. She had reached the respectful age of twenty-four, but she was clearly suffering from kidney failure. She was painfully meowing all the time, had lost control of her bladder and she no longer seemed to be... happy. She was three years older than me, and I'd been taking care of her since I was able to... so I knew it was her time. I had planned to take her to the vet to let her peacefully drift off, but they told me I was being selfish and that I just didn't want a 'defective cat'! The nerve! I had been crying for days, knowing we were going to the vet. But after that, it was so hard to go to another vet. I wish I had now, because about two weeks later she was partially paralysed and seizing badly. I had to rush her to the same vet to have her put to sleep and couldn't do anything but softly pet her as I told her it would be alright soon. It's been six years, but I still tear up when I think about the way she looked at me that day when I held her. So yes, I have learned my lesson about being adamant with a vet and I promise I will if I ever feel they are not doing enough!
I never consider that it might have slipped into her eating ritual as an unfortunate habit after years of being sick! That is a very helpful suggestion! Suffering from tics myself, I know how easy it if for something like that to slip into your routine.
The shelter was not able to give me a lot of information about her previous home, except that she, along with another kitty, had been left behind. The other one was healthier and younger and therefore made it through the adoption system some time before her. Considering that they were left behind, it would not be too far-fetched a thought that they were unwilling (or perhaps unable) to afford all the veterinary bills and food she needed. Although she has very different tasting food now, she could certainly have picked it up along the way.
In a way, it's a form of self-preservation. Whether it's a beetle that tastes bad and must therefore be avoided, or salivating because you know that you're going to be throwing up soon. It certainly makes sense! Taking that into consideration, even her odd behaviour of rubbing her teeth against stuff could be seen as her showing signs of the life she had with her previous owner. If that is all, I would be very relieved. Even if it's unfortunate that she picked up those habits due to someone not properly caring for her.
As she does seem to be completely fine after some time has passed, I believe I will hold off on dragging her off to the vet for the time being. It worries me more than it truly bothers her probably. It has taken her so long to truly adjust to moving in with us, that I really would not want to risk putting her in another stressful situation unless it is absolutely necessary. However! Considering her age, I will be taking her in for an annual check-up in a few months (maybe a little earlier just to sooth my worries). Unless she shows any signs of distress beforehand of course.
Thank you both for your responses (and sorry for my rambling). I do feel a little less worried now, although it will never entirely pass until she stops.