
It's hard, because there's this little tiny person who is the center of your universe, and you want more than anything to be happy. So you find yourself making concessions where you are unhappy but she gets what she wants, so you can keep the peace. The problem is, little tiny people grow up to be big people with big expectations that they're always going to get what they want. IMO, it's better to deal with these things when they're little. I think of the metaphor Dr. Sears uses in The Discipline Book where we think of these habits as "something they'll grow out of. But instead of shedding the old habits, they just keep piling on new bad habits, and eventually you're stuck dealing with layer upon layer of negative habits that you ignored just for the sake of keeping the peace.
Which sounds a whole lot more like Gentle Discipline than nightweaning.

But, bringing it back, it makes me think of another Dr. Sears quote-- discipline begins at the breast. If your daughter doesn't buy the whole "milkers go night night" scenario and if you can't come to a compromise that makes you both happy, it could be the perfect opportunity to teach her the word "no". I believe it can be done in a loving way, and I believe that a mother's needs are important as well.
I'm not trying to come down on you. I just think if you're wanting to nightwean AND you want it to be 100% your daughter's idea so there's no tears and no dischord, you could be waiting a very very long time. Child led weaning is great if that's something you're committed to. But gentle mother-led weaning is great too if that's going to bring some peace to your family.

Good luck! (And pardon my ramblings, LOL!)