Ok, I reckon you have 2 options: go for whichever suits you best:

1. Bite the bullet, invest in a waterproof matress protector, make sure you have loads of spare cot sheets and PJ's at the ready, and let her go to bed in just undies/pj's, and see what happens........you may be up 4 times a night changing wet linen etc, but you may not....see how you go, and how she responds to that.(It may make her miserable, or she may love it.)

2. Keep her in nappies for nighttime sleeps until she wakes up dry with a dry nappy. This may take another few years...........

Good luck either way.......