Just say "But… You're drunk." Sad puppy eyes, and slight negative curvature of the mouth. Make it beyond clear that drunken sex isn't just distasteful and possibly date-rapetty bad, but downright tedious to consider for a Love Stallion™ like yourself. If you don't know quite how to pull the above off with your existing facial expression repetoire, you can practice in front of a mirror saying "my cruise ship room service waiter days are OVER, missy" with just your eyebrows for a few weeks. Practice, practice.
Then, optionally, "Let's do things that are fun to do when you're drunk, instead!" Happy birthday clown eyes, wild grin. Run outside and try to pee on whatever nighttime fauna are available in the vicinity. Sing an entire NWA album to a random member of her cell phone's contact list. Don't take advantage too much, but don't hesitate to lightly punish the overindulgent through sheer silliness and outright mockery. It's the only way they'll ever learn. You could be indirectly saving a life every time those bloodshot eyes are caught like dazed Pokémon on someone's Facebook wall.
Be fun, entertaining, and make a clear effort to moderate between trying to sober her up a bit, and trying to keep her from hurling indoors. Call her a cab. Make sure there are enough pictures and videos that everyone at the party will remember what a wacky class act you are. You may even get a hungover thank you call the next day, which, if desired, you can be parlay into her taking you out for dinner by way of apology… And who knows where that might lead.
Homerun version: you get more than one hungover apology call. Sometimes women remember the crazy stuff that happened at a party, and just assume all that awesome was them. Feel free to date as many of these sheepish Sunday callers as you like… Just make sure to get an address from each, otherwise things might get a bit awkward when you realize you're dating roommates only after taking the second one back to her place for a naked twister nightcap (true story).