I'd go with something like:
Daisy Mae/May
Daisy Faye
Daisy Lynn
Daisy Lee
I might not pick a current "trendy" girl name as the middle name (like Sophia, Isabelle, Ava, Emma), not because there's anything wrong with them, but because then you end up with a generic name that because of the daisy is a bit cutesy (Daisy is a very girlish name) and might only suit a girly-girl.
Instead since you ARE from the south, and Daisy already sounds southern, a Mae/Faye etc. type name makes the name charmingly and intentionally fully vintage southern. It's SO old school southern that it's actually seems fresh/chic. Plus she can be a girly southern belle with it or can take it a bit toungue in cheek and be kind of spunky/funky with it.