Ask her what: how much she hated his concubine and her son? I think the Bible is pretty clear on that, actually.
What does not add up to me is that who in their right mind would want to begin parenting a newborn baby at age 60? It makes me suspicious as to whether he was really looking for a surrogate. Plus, whey wouldn't he just go back to his old surrogate or her service if he found her through one?