[name_f]Stella[/name_f] is the most obvious choice, but I’d suggest Stell! Stell is one of my absolute favorite names.
Others:
[name_f]Essie[/name_f]
[name_f]Estie[/name_f]
[name_f]Elle[/name_f]
[name_f]Ella[/name_f]
[name_f]Ellie[/name_f]
[name_f]Elsie[/name_f]
Stellie
Tellie