Congrats on your bunny! I don't think she's a mini rex mix, however. If she is, it's very little in the mix.
She's so cute!! I like her name :)
(your friend's bunny should have been neutered to reduce aggression issues) when Boo reaches 6 months old, you need to have her spayed to eliminate the chances of her getting cancer (I lost a bunny to it and it was dreadfully sad bc it's an avoidable premature and painful death). It will also eliminate the "aggression" she will grow into with puberty.