from my point of view you're on a no-win situation: she already have trust issues, what it means that there's a big chance that she might get upset and break up everything with you, because she don't believe that you're innocent and nothing else happened with that woman. And another thing, have another woman sleeping in the same bed where you're slept with the woman you love and want to spent the rest of your life with, isn't the best thing to do.

On the other if you don't tell her, she will discover soon or later, and it will mad with you and break up definitively with you.

Why on earth, would you drink really hard with another woman, alone in your house ? And worse, didn't you never heard that you shouldn't take another woman to your (you and your gf/bride/wife) bed ? Apparentely not :|

i can't see a good solution here... you might lie to her ( i can't believe i'm saying this), telling that your female friend did, in fact, slept in the house, but in different rooms. Keep in mind that she probably will not believe in that, and because it's a lie sooner or later, thruth will come out.

i can't find a good solution to your problem, at this moment. sorry...