12 year old says she wants to live with her dad !!

My 12 year old daughter text me from her dads house tonight that she would like to spend more time at her dads. We have two children together an 8 year old son and her, 12, I am remarried and just had twins 7 months ago. My ex husband and I share custody of our two children and each have them every other week, she is now telling me she wants to spend the weeks with him and see me on the weekends. “Try it out for the summer” were her words. She said she wants to live closer to her friends because at my house she is about 20 minutes from her friends and that people have asked her to babysit this summer that her dad and step mom know and they will pick her up and bring her back to her dads, she didn’t really give me any other reasons, she said she loves me very much and doesn’t want to upset me but wants to spend more time at her dads. This of course upsets me and I really do not know what to do, I don’t want her to end up resenting me and be here if she doesn’t want to be. I’m not sure if she is old enough to make such an adult decision, she will be 13 in September but part of me feels like if that’s what she wants maybe I should let her. I’m just confused and upset and wondering what to do and what the right decision on part my part is.