'I don't know' is the only answer that I can give, because this would make me feel very uncomfortable, too.
And the girl in question may well feel awkward and that she could lose her friend.
Inter-gender friendships can be great, but, sadly, they can cause problems.
Just try to be relaxed about it.
Maybe all of you could spend some time together?
You could ask your boyfriend how he might feel, if your best friend was a boy ~ and what he thinks might be the best way to go forward with this situation.