biting/aggression

Question
I am a first time rat owner. I got two young female rats about a month ago from a local Petco store. They were both in the same cage in the store and have almost the same markings, only one has black spots and the other has light brown spots, so I'm guessing they could be littermates. Anyway, I've noticed from the beginning that the one with the brown spots (whom my nephew has named Luicy) kept mounting the other one (China). She never really did anything other than that. Every now and then I'd find Luicy chasing China around the cage and then mounting her. I've read on a couple web pages that two females will/might do that when one of them comes into heat, so I didn't think anything of it. I started out having them in a 20 gallon tank, but Luicy started jumping up and hanging from the top. That got really annoying, since she did it at night and the cage was in my room. So I put them in a wire bird cage I had for my cockatiel, and I put fencing around and put a shelf up about halfway to give them a little more room. that was about 3 weeks ago. I've noticed for the past couple weeks that Luicy has been chasing China around and nipping at her more frequently. Another thing I've seen from the very beginning is Luicy chasing China around and pinning her down, or I guess what you would call "force grooming." She's definitely the dominant one out of the two.
I've heard one of them squeaking a few times before (not very loud, but loud enough to hear) and I've caught Luicy biting onto/pulling on China's fur a couple times. I got China out today to play with her and I noticed she now has a couple scratches or bite marks on her tail. I'm not really sure which they are, but I do think they're bite marks. They're not very long, or at least enough to be scratches.
I'm not sure what to do about Luicy. I've been spraying her with a squirt bottle every time I see her chasing China around or when she starts biting at her or starts fighting with her, but it doesn't really seem to have much of an effect on her.

Answer
Yes, it is normal for there to be an alpha female and for her to "power groom" her friend. As long as no one is getting more serious cuts or injuries, these little scratches are nothing to worry about. As for the squeaking, this also is normal, just like its normal for two young siblings to fight. I understand how worrying these things can seem, but try to remember they are normal.