I think your family's actions by being there for Jamie during her time of need is wonderful and a lovely example to your children on giving love and acceptance to others.
She is still a child.
Whilst you may feel betrayed you cant let this get to you, keep your heart open, show your daughter being love is more important and maybe there are more lessons to be learnt here like boundaries? Or the ability to walk away from situations that are not good for her ... life will present these situations to learn and hopefully grow from.
"Your mommy heart is broken.." maybe for now. All I know is you sound like a very loving and caring person and mother so dont let yourself dwell on it too long.
My answer is way too long so thank you for sharing! I feel like I know you and you write like I am listening to you tell me a story over a coffee