What, crying at a wedding ;-)

I'd say, keep it pretty neutral in eye makeup and maybe some nice red lipstick. Not sure what look you're going for tho. If your eyeliner is waterproof, you should be set, right? Or, you could put the Shelack on there (depending on where), to seal it. I'd test it out today. Play around with looks and how it goes with your outfit.

Good luck and have a great time at the wedding!

Are you Bridesmaid and dancer in costume, or just bridesmaid, and there is other entertainment?
If you are performing, then do a sleek, minimalist interpretation, to enhance the black/white contrast.
If you are there as guest and to be your bride's "right-hand girl", Neutral shadow, using the pale/white at the inner corner of the eyes to highlight, and simple liner or a variation on the smokey eye look is clean, classy, and will look great in photos. You want to look good, but don't overdo it, it's never cool to outshine the bride.

Waterproof liner and mascara are a must, don't worry about lining the waterline or under the eyes if you think you'll cry. Remenber to bring a little travel pack of tissues. throw a few bobby pins, safety pins, and oil blotters or a powder compact in a little purse, just in case you or the bride needs it. maybe lipgloss, mints, and a travel-size hairspray if it fits. Remind your bride to drink water during the day, sometimes we forget little necessities when we're having such a big day.

Having been a bridesmaid twice, once as maid of honor, and a bride myself, just be there for her, and enjoy the day. Congrats to your bride for her big day, and being lucky to have a great friend to share it with. If you can fit one more thing in that little bag, keep a camera on you, and take a few candids throughout the day. you'll both treasure them later.