I like Peyton as a girl’s name or a boy’s name. I think I would spell it Peyton for a boy and Payton for a girl, but that’s just me! It’s a great unisex name, even though it’s normally a boy’s name.
Since Peyton/Payton is unisex, I would suggest using a feminine name as the middle name. Just to give her options, but it’s really up to you. I don’t mind boyish/unisex names like Casey or Jordan used on girls and Lindsay is definitely a more feminine, but I find it ridiculous that someone would name a sweet little girl Michael. That’s so masculine. Unisex names are strong enough for girls, I don’t think we need to take old fashioned male names and claim they’re ‘unisex’.
Sorry if I used common middle names!