Now this is a VERY long time ago but my parents split up when I was 2 and even though I was an only child I distinctly remember having tantrums and meltdowns whenever my mother even remotely showed affection or gave compliments to someone else. I recall I was around 5 or 6 when the feelings peaked. I did grow out of it without any help but that was 30+ years ago and help fo rthings like that probably weren't around.

So I think that it is very understandable given what she has been through and I would encourage some counselling for her to help her get through this and help her manage her feelings. However, I also think that she will get better as she matures.