I say feed her. Perhaps get in touch with a local feral organization and see if you can arrange for her to be trapped and spayed.

Everyone in our apartment complex used to feed the ferals by the dumpster...that's probably how I got my Scout...the kitten from one of the ferals...who was too dehydrated to put up a fight when he curled up outside my doorstep. Our complex became really strict about feeding them..putting up notices, asking people to report anyone seen feeding the cats (it was ridicuolous)..heck when I read my lease again, it specically states that we are not allowed to feed any stray animals on the premisis. I don't feel to bad though. ...there is a sushi and steak restuarant in front of our building and the bus boys took a liking to our 3 ferals. If it wasn't for that, you can bet for sure I'd still be putting a little extra cat food out.