August and Norah are so sweet and Robin goes so well with them! I love Mabel and she works perfectly, I don’t think of her being very trendy but here are some other ideas 
:
Mavis
Pearl
Hazel
Lucy
Rose
Violet
Etta
Louisa
Eloise
Thea
Pippa
Clara (Maybe too close to Norah tho)
Olive
Odelia
Opal
Ruby
Dahlia
June
Mina
Sadie
Poppy
Molly
Calla
Della
Sorry for any repeats!