Will a female rabbit try to mate another female rabbit?

Yes, they will try to mate with each other. They are signaling to a buck that they are ready to breed. They are not actually trying to breed. BUT every rabbit should have it's own cage so how is this happening?

Another opinion: Rabbits of both sexes sometimes mount another rabbit as a show of dominance. Mounting isn't always a sexual behaviour. One female mounting another is trying to assert dominance. Keep an eye on your bunnies and separate them if it turns to fighting.

Rabbits can be kept in the same cage if they're bonded. Usually this means the rabbits must be neutered/spayed - but, in some cases, when they've been raised together, female rabbits can be kept together even when they aren't spayed, and they won't fight. When rabbits are bonded, that means they don't fight and are affectionate. The bonding process can take anywhere from a couple weeks, to many months of patience and hard work.

See the related questions below for more info and links.