I understand that Lady Selyse Baratheon is a little off her rocker, but is there a particular reason that she appears to hate (or at least, strongly dislike) her daughter Shireen so much? Surely she can't blame Shireen for her face, which - as the result of getting Greyscale as an infant - is no fault of her own OR the child's. Stannis himself doesn't appear to bear the child any ill will.
The only thing I can figure is that Shireen is a reminder of her failure to provide Stannis with a son, something that he desperately wanted. Is this the case?