@Kghl03
Okay here's a few more... tried to prioritise a cohesive rhythm and sound so not sure if they'll still be to your taste 🤍 if you prefer the spelling Isabelle, like those names, and love Fleur, then I think going down a gently French route will be the best option. Most of these are French or anglicised French names (with the original French in brackets) with a couple of other wild cards thrown in there as well.
Isabelle Marie Graham
Isabelle Sophia Graham
Isabelle Felicity (or Félicité) Graham
Isabelle Noelle (or Noèle) Graham (you'll love or hate the "Elle" repeat)
Isabelle Cordelia Graham
Isabelle Cosette Graham
Isabelle Camélia Graham
Isabelle Violet (or Violette) Graham
The names Michelle and Natalie are relatively common but if you committed to the French spellings of Michèle and Nathalie they become more fitting with the overall name so do have a look for French versions of names as well (and make your decision about whether to go for ones that need accents or not).
You can also consider some Italian or Spanish sounding ones, but their spellings of Isabelle are Isabel and Isabella respectively so consider if you would prefer name origins to match or contrast.
Isobel is a Scottish spelling, which I only just learned but you may already know, so if you go with that spelling it might influence the middle name options too.
Let me know if you want any more ideas!