If her teeth are fine, is there a reason you hand feed her? Does she have trouble eating on her own?
Most guinea pig books and magazines are full of misinformation, unfortunately. I wouldn't feed banana at all, it can cause constipation. Fruit should only be fed once a week (that would include any apple sauce or baby food).
This thread has a bunch of charts on which veggies are good to feed as well as some other information
and this thread has some sample menus. Pigs are often slow to try something new, so even if she doesn't eat something right away keep offering it to her. It may take several weeks before she decides to eat it.
If you don't trust that she's getting enough food on her own and you think she needs to be handfed, I strongly recommend
Oxbow's Critical Care. I wouldn't feed baby food, I've heard of people having problems with bloat when using it.
If she eats a varied diet, following the rules provided by Ly's chart, she shouldn't need any vitamin C supplement. If she's not eatting her veggies right away you can syringe her som
liquid vitamin C. 30 mg should be more than enough a day.
I leave my girl in her floor time pen sometimes for the entire day. She loves having all that extra space to explore. I'm sure your girl will be fine as long as the pen is stable and she has food and water.
When you look to adopt her a friend, perhaps you can find a guinea pig rescue near you to help you pair her with someone. All the handicape pigs I've read about feel much safer when they have a good friend to touch and smell.
(Sorry this post was so disjointed, I was trying to answer all your concerns so I was scrolling up and looking at your two posts to see if I missed anything).