the others are right. Don't make a big deal out of it - just drop her a line, ask how they all are etc, and then just say that your mother had been talking about the photographs the other day again, and you recalled that she had them and wondered whether you could borrow them to get copies made for your mum. don't be accusatory as you'll end up not getting the photos. I'm not really sure that there was anything vindictive in your cousin taking the photos - presumably there's some of her father as a child in amongst them.