Can you experiment with her either almost sitting up or lying down and see if either of these help?
I had to take my 4 month old to lactation day stay because he had got strong enough to hurt like heck - it turned out for me that the underside of my nipple wasn't actually going in his mouth. The LC also pointed out that they start to copy you as they get a bit older - so if you make big open mouth faces then bub may do so too.