Remarried

I told my daughter I was getting remarried . Now she acting all strange. My youngest daughter(15 years old) recently lost her dad in January and he was my last husband but we divorced years ago.She says she's going to move out and go live with her auntie on her dad side.She goes in her room and shuts everyone out .She won't eat either. I understand she don't like her step dad and she can hold a grudge for a very long time . I don't want her to think I'm trying to give her a new replacement dad. I don't know what to do .