Good grief,give me an animal over some people any day.Your DIL obviously got a problem with something,but then it's very common,maybe its women in general,some are so insecure,maybe it's to do with you and your daughter,perhaps she's resentful,
I've found out over time,my own DIL had a traumatic upbringing,that's why she's so unstable and insecure. I just step back now,let her be,she usually comes round.[she knows how much the kids love me,nobody could look after them better]
Leave her,just go and see the children for a couple of hours.Some of these women want it all their own way.
Step back,be there if your needed,be nice and friendly so they can't accuse you of anything,but stay in the background,shower all your love on the kids.
Mine as soon as they think I'm getting ready to go.