She's a cutie. I think your first guess of 6-7 weeks is probably closer. Her ears are fully up, they'd be floppy on a 4-5 weeks old still. The eye color is tough to tell, from your pictures, but they don't look deep baby blue to me - baby blue eyes also have murky pupils. My best guess would be 6 weeks.
I think you'll be fine with the kitten food, if you haven't opened the KMR you can return it. I feed my foster kittens at that age about 1/2 small can per day - but they're usually nursing off mum and eating kibble as well. I'd say start with 1 small can per day, in about 4 meals. I'd put kibble out for her too, to see if she knows how to eat it and to give her some extra calories.
As far as socializing her, I'd suggest going in and cuddling her twice a day at least. Pick her up and place her on your knee facing away from you (wear jeans
) then use one hand to prevent her from jumping off - you might need to scruff her at first, but it's better to just hold her firmly instead. I use three fingers tucked underneath from one side - two meeting around her neck and the third to hold just behind her front legs. Use your free hand to scratch and pet her, if she relaxes then relax your holding hand, but don't let her escape. Once she's calmer and has relaxed a bit gently set her down - don't let her jump off!
I also like to read out loud to feral or nervous kittens, especially while they're eating. This associates your voice with food, and helps them get used to the tones you use, without your eye contact making them nervous.
Spend a LOT of time socializing her now, just sit nearby and let her get used to your presence at first, so that she becomes more social quickly. The faster she gets used to you, and then to other people, the more social she'll be as an adult. It looks like she won't be a tough case though.