Id have retorted with well there could be some gratitude shown you're way for all the work you have both done for them all, as for not liking you I'd have said that the feeling was mutual and that you have only done any of this for the grandkids and not for her or your boy as they are old enough to make they're own decisions.
But thats twopence worth and if I get the gears in motion and meet the bitch I'll tell her as much in person followed shortly by kidnapping her and disposing of her in some desolate hovel in the middle of nowhere