As long as she's not being rough with her, let her play however she wants. It's her doll and that's what dolls are for!

When you get Felcity for yourself, you could let it be known that it's YOUR doll, which means she can only play with that one if she asks you first. But I think her own doll should be hers to play with however she wants.

Josefina is not going to stay as nice as she was when she was new, but that's just part of what happens...the best-loved dolls are always a little worse for wear, it shows they've been played with..

Just make sure she's not being too rough with the doll like climbing up trees with ehr where she could fall and ruin, or getting stuff on her "skin" like paint or dirt, etc.
And that she's not being too rough with the hair- oh that is a big one. Let her do the hair but teach her how to do it the right way (a tag attached to the doll's wrist tells how to do it correctly) and encourage her not too be rough with the hair or even to do the hair too often- because you cannot get just a wig replacement from AG- you have to replace the whole head. And when she is older she won't like the messy fuzzy hair but she will not want to replace her doll's head either. So the hair is really the only thing I would be worrying about too much.

Remember in one of Samantha's books, when Sam sees Lydia, her new doll that she had given away to Nellie?
She sees that Lydia's dress is wrinkled, her buttons are loose, her face is smudged, etc. (I'm not sure if those are the exact things wrong but anyway in the book they list several things that look bad on the doll)
And then after listing all these things wrong with the doll, it says: Samantha smiled, she knew Lydia had been loved.