First of all, the gray linty-looking stuff is faux fur fabric that she has spread out on the bottom of the cage.
Secondly, she isn't- wasn't when I got her- with other rats. I don't ever plan on putting her with other rats since a majority of my rats are males (and that would fail to be a good choice).
Concerning the fact that she's from a pet shop and a "feeder" - I knew she was a feeder when I got her so I'm really not stuck with her and I prefer not to be involved in the pet store versus breeder controversy. I know that health issues are a concern as is lack of socialization but I feel that she should be given an equal opportunity to prosper. I know it will take alot of time and effort but I'm willing to give it a chance.
As for exercise and care, she definitely doesn't lack either. I have a separate pack and play just for her with toys and such.
I'd like to say thanks to everyone for the ideas. I know that everyone may not agree on certain rat topics but I think we can all agree that no matter who the rat is or where it came from we all just want to give them the best care possible. That is why I joined this community and I appreciate everyone's ideas and contributions.