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Cats can definitely get into scraps with one another. Usually it is 2 males that will act this way towards each other. Males will also kill kittens with no problem, but an adult female I doubt it unless she was on his turf.
There are several animals that will attack cats depending on where you live. Things like raccoons, possums, foxes, and coyotes if you live in an area with them .
No matter what did it, you need to get her checked out by vet if not done yet. The risk of infection from animal bites and scratches is very high (over 90%), and an antibiotic is needed to prevent this from happening.
Let me know if you need any more help.