I dunno, given the versatility of her powers I'm pretty sure Grace can replicate any non-fatal fetish that exists...well, maybe macro, I know she can turn into a tiny little squirrel but I don't know how big she can make herself.
As far as I recall the height limit is somewhere at 110%. She can just transform into a tiny squirrel, because it's inherent to her. As far as her transformation skills go, I think she can mostly change aspects about herself and cross them with animal aspects, but neither can she change into a cartoon My Little Pony on a whim nor can she take on the physique of a tentacle monster nor can she change herself into sentient pudding.
I agree that she can tackle more fetishes than many people reasonably could (and if she hasn't already played some of them out with Tedd in private, I am very much certain that they will when they're older), but that character is far away from being a walking, talking fetish machine. Just remember: One man's nightmare is another man's fetish. Like doorknobs. Or the sound balloons make when being rubbed against skin. Or Captain Buggy.
Graces additional abilities (beyound squirrel forms) is from the TF gun. It's just assumed at this point that her and Tedd have messed with it to an amazing extent. So pretty much anything is on the table except what's outside the limitations of the gun.