If she willingly came inside she is most likely not feral. A feral cat is wary of people and distrust us and probably would not willingly come near us or in our homes. If this cat is sociable and friendly she (or he) is probably a stray or someone's pet that got lost. If she is friendly and/or has tags, then take her to a local shelter or vet and see if they can scan for a microchip. If no information is available, you could put up posters or flyers to see if anyone responds. In the meantime, you can provide food, water, shelter and a litter box. As a university student you probably don't have much extra $$$ so keep that in mind as the cost of keeping a pet can be significant.