Someone with more rabbit know how may be along soon but I would think that you should isolate the new rabbit for two or three weeks initially ..... in case of contagious disease transmitting to your pet from the new rabbit. Also check for external parasites.
I would then separate the hutch/pen with strong wire so that the rabbits can see each other but not have contact or put them in separate hutches side by side ..... again so that they can see each other.
You should introduce ideally on neutral ground ..... otherwise there could I imagine be a serious fight.
Hope that helps. Not introduced many rabbits myself but my sister has many times and used the above approach. I think hers were all neutered though. Don't know enough about rabbits to know whether two entire females would live peacefully together.