G.♣.
I have no personal experience, but it is my belief that this is way beyond the scope of what a 7 year can comprehend. If she thinks she wants to live with her father, it's because she had a great weekend and things with you have been a bit blase this week. Or it's because she got in trouble earlier today (or earlier in the week) and has it in her head that Daddy wouldn't be as strict. Perhaps it's because when she's with Daddy she gets to watch a lot of tv and eat junk food while you make her eat healthy, limit her tv and enforce a strict bedtime.
She is not old enough to know what's best for her. What she sees as a "need" is most likely very superficial. Just smile and say, "Do you miss Daddy?" or "Did you have fun this weekend? I'm so glad."
She is way too young to know what's best for her.