Something wrong with my cat?

Ok I have two female cats. Both are 11 months old and from the same litter. Last night one of them got outside and was out for about 2-3 hours while i wasnt home. (I havent had them fixed yet.) So I get home and she is curled up against the wall outside my apartment. I figured she was just scared. So I take her inside and put her with the other cat and she begins to growl at her and the closer she gets she begins to hiss. I tried letting them smell each other and everything but she refuses to go near the other cat now. So I am just giving them time and before long she starts cleaning herself. While she is doing that I notice her anal area is extremely red and and sticking out. Could she have mated with another cat or what could be wrong...pla any help appreciated

by a Tom. And at her young age, the anal portion depending on the size of the male that got her, was stretched. If you don't see improvement soon, I would take her in to the vet, because she could develop some problems when it comes to elimination and such. You can also get her spayed too, such a young kitten should not give birth.