Welcome to the world of cats!

Sometimes it's hard to tell whether your cats are playing together or if they're getting hurt... I have two male cats myself, and they play endlessly every day until they get tired and sleep. Sometimes, they bite and scratch and wrestle, but they both seem fine at the end. If your little girl is hissing, that may be a sign of intimidation. Usually, two male cats are better off than a mix of male and female (personal experience). I think you should test the waters a little more, see if she has any physical marks on her (my cats play all the time and there are no physical marks of being hurt), show her lots of love and introduce other toys for them to play with...

If she still seems to be being attacked by the male, it's probably best to separate and try get a male. Sometimes, cats just don't need a play buddy and are satisified being alone. Naturally cats are loners, so that is not uncommon.

I hope that helps!