I agree with the others, Gabrielle is too overlapping. I also don’t like Gabby or Gabs etc.
I love Anastasia - not too long, same syllable count and only one letter more than Isabella. Anastasia Juliette would be very charming and a regal pairing with Isabella Victoria.
Others:
Francesca
Theodora
Charlotte
Prudence
Josephine
Tallulah
Georgiana
Cecilia
Seraphina
Celestine
Tabitha
Hermione
Rosamund / Rosalind
Clementine
Anoushka
Willamina
Evangeline
Marguerite
Bernadette
