[name_f]Cece[/name_f] would be my choice! I think [name_f]Celie[/name_f] (if it’s said like SEE-lee?) is super cute? I don’t like the sound of sell-ee though.
[name_f]Estie[/name_f] is super cute, too. I’d probably rank them Cece, Estie, then Celie. Lessie/Lissy is nice but I like [name_f]Lissy[/name_f] way more than [name_u]Lessie[/name_u] personally?
Besides Cece, I think Essie, Sia/Cia/Lia, Cella, Ella/Ellie/Elle, etc., could also work.
Good luck!