If Quirrell were female, "he who stands within" would refer to someone else, since "he" is masculin.

That's pretty unlikely, though, since he's apparently keyed into the wards as a professor, so far as anyone can tell.

(Quirrell keeping a troll shrunken/in hammerspace on his person at all times is my favorite explanation at present, even though it sounds like it should have a silliness penalty. He did mention the Hungarian Horntail in the same lecture where he mentioned the troll, and this particular theory would give more credence to the idea that he has one of those hidden somewhere as well.)