If you already know each other well and you're friends just tell her how you feel (without being drunk). The worst thing she can say is that she isn't interested in you in that way. Things might be awkward again for a while but since you've been through it once and maintained the friendship there's a good chance that the friendship would survive again.
Have you given any thought as to what will happen if you do embark on a relationship with her and she develops feelings more strongly for one of you than the other? Although triads do form and are successful more often than not feelings don't develop equally among all partners. Be honest with yourselves and with her about what that will mean for you down the line once you've gotten the immediate conversation about your feelings out of the way.
Everything will be ok in the end. If it's not ok it's not the end.