Congratulations! 3 girls is so special! I have 3 girls and also found it so hard to name the last one, i too felt like I’d seen every name ever come up with.
In the end we ditched the expectation/pattern and went with a wildard name that was kinda off brand, but we love it. So I hope that helps…
Some suggestions:
On brand for you (vintage/nicknamey)
Opal (still a colourful name but not very popular and not another flower name Polly as a nn option)
Bonnie (vintage nn and so sweet and happy)
Zinnia (bright and zippy floral)
Acacia
Lenna
Etta
Amaryllis (nn Rilla, Amy, Lissi)
Joni
Sally
Off brand/ wildcards
Suki
Cadi
Liv
Astoria
Farrah
Neve
All the best!