My female mice are fighting and I don't know why.?

Its because you bought them at differwnt times. Since mice are usually sold often, the mice that Lila was with at the store were long gone by the time Misiu was bought. Since the mice would not be fromthe same litter, they would fight. If the mice are fighting and they are getting hurt, you should separate them immediatly. If they are just play fighting, and they arnt getting hurt, I would just ignore it.