For the nickname [name_f]Posy[/name_f], how about…
[name_f]Calliope[/name_f] [name_m]Lacey[/name_m]
[name_f]Calliope[/name_f] [name_f]Mariposa[/name_f]
[name_f]Calliope[/name_f] [name_f]Giselle[/name_f]
[name_f]Calliope[/name_f] [name_f]Jessamine[/name_f]
[name_f]Calliope[/name_f] [name_f]Tirzah[/name_f]
[name_f]Calliope[/name_f] [name_f]Florence[/name_f]
[name_f]Calliope[/name_f] [name_f]Daisy[/name_f]
[name_f]Calliope[/name_f] [name_f]Larkspur[/name_f]
[name_f]Calliope[/name_f] [name_f]Zara[/name_f]
[name_f]Calliope[/name_f] [name_f]Adeliza[/name_f]
[name_f]Calliope[/name_f] [name_f]Ilse[/name_f]
[name_f]Calliope[/name_f] [name_f]Therese[/name_f]
[name_f]Calliope[/name_f] [name_f]Aster[/name_f]
[name_f]Calliope[/name_f] [name_f]Liliosa[/name_f]
[name_f]Calliope[/name_f] [name_f]Dulcinea[/name_f]
[name_f]Calliope[/name_f] [name_f]Lotus[/name_f]
[name_f]Calliope[/name_f] [name_f]Nastia[/name_f]
[name_f]Calliope[/name_f] [name_f]Yasmine[/name_f]
[name_f]Calliope[/name_f] [name_f]Zinnia[/name_f]
[name_f]Calliope[/name_f] [name_f]Blossom[/name_f]
[name_f]Calliope[/name_f] [name_f]Zosia[/name_f]
[name_f]Calliope[/name_f] [name_f]Celeste[/name_f]
[name_f]Calliope[/name_f] [name_f]Anaïs[/name_f]
[name_f]Calliope[/name_f] [name_f]Zipporah[/name_f]
[name_f]Calliope[/name_f] [name_f]Selah[/name_f]
[name_f]Calliope[/name_f] [name_f]Wisteria[/name_f]
[name_f]Calliope[/name_f] [name_f]Estelle[/name_f]
[name_f]Calliope[/name_f] [name_f]Anneliese[/name_f]
[name_f]Calliope[/name_f] [name_f]Sunday[/name_f]
[name_f]Calliope[/name_f] [name_f]Ines[/name_f]
[name_f]Calliope[/name_f] [name_f]Astrid[/name_f]
[name_f]Calliope[/name_f] [name_f]Elsinore[/name_f]
[name_f]Calliope[/name_f] [name_f]Lucille[/name_f]
[name_f]Calliope[/name_f] [name_f]Thalassa[/name_f]
[name_f]Calliope[/name_f] [name_f]Sarah[/name_f]
My thinking is that floral names reinforce the theme and ‘c’ and ‘z’ could work sound wise.