When you buy sunglasses for your baby, make sure the sunglasses can fit her properly. If the sunglasses are too tight for them, it will pinch your baby's face, which make her feel uncomfortable. So she will try to remove the sunglasses from her face. But if the sunglasses are comfortable to wear, they are less likely to remove them. Or you can get a strap to help hold the sunglasses in place.
You'd better don't make your baby wear sunglasses. Baby's retina is growing, sunglasses keep off the sunlight, it is not good for the growth of retina. And if you still want to let your baby wear sunglasses, you should pay attention of the quality. Even thought it is very expensive. and remember that take off it as soon as possible.