I struggled the first few days too due to big breasts. She has to make sure she shapes the breast with her hand and guide it into babies mouth. Also with big breasts you have to keep holding and shaping the breast as you feed. The weight of the breast pulls downwards and if you don't hold it the nipple will slip and destroys the latch. Also get her to stimulate the nipples as much as possible and squeeze a bit of milk out to get the taste of the milk on baby's tongue.
That's all I can think of right now... will update when I think of more!