why does it all change in a second

i was in quite a good mood today,even found myself laughing at times.but then our daughter decided for some reason she wanted to unblock the bitch on facebook and then tell me really hurtfull things wich i asked her many times not to do.why does she feel the need to upset me in this way?i asked her the other day to please think about what she says and does for the time being,just until im feeling a bit stronger.shes now saying she is going t text him and say she wants to go and stay with them,im not the one whos walked out on her and started a new life and no matter how much im hurting im there for my kids,i do everything for her and i always have.