hair loss in cat

hi everyone! i have been feeding an outdoor cat for a few months now (she refuses to come inside with my own indoor cat) and today i noticed significant hair loss around her neck. i have an outdoor house for her if she gets cold, and i feed her the same diet daily of both wet and dry foods. i have a picture attached of the hair loss around her neck. i haven't noticed it before today, and it makes me very nervous. it isn't a spot she could lick... does anyone recognize what this might be? it is going all around her neck, although only a few clumps/patches of hair still exist to break up the baldness. could you please lend me some advice?

Since she is longhaired and probably has not been combed regularly, chances are that she got mats around her neck and has scratched them out,pulling all the hair with them.  I does't look like she has any obvious skin lesions (i.e. red circular lesions or yellow flaky areas) at least from what I can see.  Watch the areas and if it was just pulling out mats, new hair will start growing in the bald patches to replace what was lost.  If the skin starts showing any kind of lesions, however, see if you can lure her into a carrier and take her to a vet.  Good luck with her.  She is a lovely cat.

First guess, a healed abscess. It's not red or inflamed and the skin looks okay in the photos. If she had an abscess in that spot and it created a scab the fur might have fallen out when the scab fell off. I know that happens with my sister cat when he has abscess. If it is that then there is nothing to do but wait. 

Second guess, is some sort of bug bite and the hair is falling out as a reaction to it. The skin may fall off next as the area dies. If she allows touching you can try petting it to see how it feels. If it feels like a dry scab then this is more likely and the top layer of skin will likely fall off. If you start to notice that the area is turning red then she may need antibiotics to prevent infection. Neosporine might work if she tolerates it; because of the location the risk of her getting sick from licking it is low. If it gets red and spreads she needs to see a vet because it could be a more serious spider bite and those can kill if infection sets in. 

Third guess, ringworm. You'd know that because it will spread without going red and she may start having other spots. Vets can confirm but if she is feral it is more difficult to get a confirmation on. I am not sure how important it is to treat ringworm in ferals. I know it spreads easily but it tends to become a problem on cats with weakened immune systems. It also requires more invasive treatment option though and can be passed to humans. 

Best action right now, wait and see what happens. If it grows, time to consider trapping and a vet. If it turns red, you definitely need a vet to prevent infection from setting it. You might need a temporary housing for her if treatment is needed. It might also clear up on its own with time if my first guess is right.

Edit: that mat guess is also a good one. I've never had long hairs so didn't come to mind.