Well I must first admit I've already been feeding it all week. It appeared
very bony when I first started, but looks more like a normal kitten now.

My concern is that this may be a female and that she will be bringing me
loads more kittens to feed if she is not fixed. (I am way allergic to cats
and couldn't have even one in the house) She runs away on approach, but
stays within sight if she expects I will put a bit of food out for her.
Suggestions?