squabbling sisters!

Question
hello, i have three, one year old, female rats all of whom are very different
from each other. one is very gentle, sweet and confident. the second is about
the same but likes her own space sometimes. the thrid however has always
been quite grumpy, doesnt really like to be held, eats all the food, very quiet  
and unadventurous when let out to play. when they are alone in the cage
together they constantly push each other around, squeak loudly and the third
rat tries to mate with the other females. she has always done this but she is
now becoming more aggressive about it and i have to distract them. i have
owned dozens of rats in the past and none have been like this.
they still eat and sleep together but they seem fed up. should i separate the
third rat? find her a new companion? feed them different food?
please please help!! thanks

Answer
It sounds like you've got an alpha on your hand. As long as no one is getting hurt, she's probably not a problem. The "mating" is just a way of showing dominance, and its normal for rats to play and squeak. If it really gets out of hand, spaying is always an option for "over hormonal" females, but it is a decision you should think about about carefully as it is fairly invasive.
Good luck.