Unfortunately I am going to say that I think its cancer/age marks. It has probably been caused by an issue with the glitter starting the break down in the plastic itself but I do think from the colour and positioning, not to mention that you say she has them elsewhere on her body, that it is cancer. I am so sorry to say that we don't have a way to cure it as yet...pony science has not cracked it too date. But I am sure she will still look lovely on display.