She probably cared more than he himself did, really. It typically takes some doing for Merlin to form much attachment to individual people. The combination of being a halfbreed and being immortal tends to enforce that a bit.

"Do you think that would make a difference if people were? After all, so far it seems that the only things possible to do in this place so far all fall into a very limited range."

And if his incubus powers don't work, well, then he can't feed that way in the first place, so there's little point in trying.