[name_f]Josephine[/name_f] nn [name_u]Jo[/name_u] would be a perfect sibling name!
Other ones that seem like a good fit are
[name_f]Roberta[/name_f] nn [name_u]Bobbie[/name_u]
[name_f]Winifred[/name_f] nn [name_f]Winnie[/name_f] or [name_u]Freddie[/name_u]
[name_f]Georgia[/name_f] nn [name_u]Georgie[/name_u]
[name_f]Wilhelmina[/name_f] nn [name_u]Billie[/name_u]
[name_f]Stephanie[/name_f] nn [name_u]Stevie[/name_u]
[name_u]Antonia[/name_u] nn [name_u]Toni[/name_u]
[name_f]Frances[/name_f] nn [name_u]Frankie[/name_u]
[name_f]Juliet[/name_f] nn [name_u]Jules[/name_u]
[name_f]Louisa[/name_f] nn [name_u]Lou[/name_u]
[name_f]Lenora[/name_f] nn [name_m]Lenni[/name_m]
[name_f]Matilda[/name_f] nn [name_u]Matty[/name_u]
[name_f]Maxine[/name_f] nn [name_u]Max[/name_u]
I absolutely love @Harvest-Endellion suggestion of [name_f]Leonora[/name_f]. [name_f]Theodora[/name_f] & [name_f]Leonora[/name_f] would be gorgeous
[name_f]My[/name_f] immediate thoughts for [name_f]Theodora[/name_f] sister with your criteria are [name_f]Harriet[/name_f] (Hattie, [name_u]Harry[/name_u] [name_f]Harriet[/name_f] means ‘home ruler’), [name_f]Juliet[/name_f] (Jules and [name_f]Juliet[/name_f] means youthful) and [name_f]Winifred[/name_f] (Freddie and [name_f]Winifred[/name_f] means ‘blessed peacemaking’) I think all three definitely work for you guys!
First of all, congratulations on the baby girl
[name_f]Theodora[/name_f] and [name_f]Acacia[/name_f]
[name_f]Theodora[/name_f] and [name_f]Alexandria[/name_f]
[name_f]Theodora[/name_f] and [name_f]Magdalen[/name_f]
[name_f]Theodora[/name_f] and [name_f]Cosette[/name_f]
[name_f]Theodora[/name_f] and [name_f]Clementine[/name_f]
[name_f]Theodora[/name_f] and [name_f]Cressida[/name_f]
[name_f]Theodora[/name_f] and [name_f]Samira[/name_f]
[name_f]Theodora[/name_f] and [name_f]Fantine[/name_f]