I don't know if we do. I kind of like the idea that we feed her but are not responsible for taking her to the vet (and the expense thereof) and such. On the other hand, you'd have to see her out there on our deck to understand what I mean about how sad she always looks. She's eating more than ever since the lady across the street moved away, so I suspect she's lost a source of food.
Good for you for taking an interest in her, but the problem with just feeding but not providing vet care is that if she's not spayed, you're feeding her just enough to keep her in breeding condition, so that creates more baby kittens and the problem multiplies. Secondly, without vaccines, you're leaving her vulnerable to diseases like feline leukemia and feline AIDs which endangers other cats, and without a rabies shot she becomes a potential rabies vector. Plus, I can imagine that she's often hungry, cold, full of worms, ticks, fleas and other nasties like that.
If you're going to maintain her as some sort of feral outdoor cat, you may want to at least humanely trap her and get her to a vet for spaying and vaccinations. Also, if you haven't done so already, provide her some kind of shelter, like a small dog house, where she can get in away from the elements.
Here's a link with info from the Humane Society of the US with tips on maintaining an outdoor cat:
http://www.humanesociety.org/issues/feral_cats/tips/caring_feral_cats_winter.htmlI worked at the animal shelter for years, and saw a lot of these cats. It's sad.