It may be time to give these girls separate quarters.
Yes, it can be dominance behavior, or it may indicate that the doe is now fertile. Rabbits don't do "heat" like a lot of animals do, but their hormone levels do fluctuate, and a doe at a hormonal peak may mount other rabbits, scent mark and/or pull fur.
Some does do become fertile around 12 weeks - it's the reason we are so adamant about separating bucks and does at 8 to 10 weeks. But just because she
can get pregnant doesn't mean she
should; you should still wait until she is 6 months or more to breed her.
If the does seem to be getting along otherwise, they may be able to continue to live together, but some get rather nasty when adolescence hits. I have had does that lived peaceably together for years, but I also had a doe that took a postage stamp-sized piece of skin off the backside of her "best friend in the whole world" at this age - so watch them. False pregnancy is another concern - if the doe being mounted is also fertile, she can experience one.
Things may be going on that you don't see, so look for signs. If you see fur all over the place, they may be fighting; if it's all in one corner, someone may be having a false pregnancy. That's not as big a deal as a doe getting bred too young, but a doe that thinks she is already pregnant usually won't breed, which can be a nuisance when you want to get her bred for real.
And of course, there's the classic - are you absolutely, positively, 100% sure that this rabbit is a doe? Even very experienced rabbit breeders occasionally make mistakes sexing young rabbits; it's the reason we joke about getting visits from the "sex-change fairy."