I like the name [name_f]Rowena[/name_f], and I was just wondering… Nicknames?
I kind of like [name_f]Ro[/name_f]. You could probably also get away with [name_f]Wendy[/name_f].
I second the suggestion of [name_f]Ro[/name_f]. [name_f]Winnie[/name_f] seems plausible as a nickname too.
[name_f]Ro[/name_f], Rowie, [name_f]Winnie[/name_f], [name_u]Ronnie[/name_u]
[name_u]Rowan[/name_u]? Actually I’d use that in place of [name_f]Rowena[/name_f], though.
[name_f]Ro[/name_f], Wen, [name_f]Winnie[/name_f]
Yes, I knew I [name_f]Rowena[/name_f] in school who changed her name to [name_u]Rowan[/name_u] and we all called her [name_f]Ro[/name_f].
Hmm maybe [name_f]Rena[/name_f]?
I’ve always like [name_u]Wren[/name_u] as a nickname (presuming you’re pronouncing it [name_f]Ro[/name_f]-WEN-ah though).
[name_u]Rory[/name_u], [name_f]Winnie[/name_f], [name_u]Rowan[/name_u], [name_f]Ro[/name_f], [name_f]Rina[/name_f]/[name_f]Rena[/name_f]… [name_f]Winnie[/name_f]'s my favorite. 
Roo, Row and Wee [name_f]Winnie[/name_f] 
[name_f]Ena[/name_f] (N-a), is my absolute favourite! I also like [name_f]Ro[/name_f], Roo, En (N), [name_u]Ren[/name_u], [name_f]Winnie[/name_f], Eny (N-e)
I adore [name_f]Rowena[/name_f] (it is on my short list). [name_m]How[/name_m] about: [name_f]Ro[/name_f], [name_f]Winnie[/name_f], Wen, Rowie, Wennie?
Roo or [name_f]Winnie[/name_f]. [name_u]LOVE[/name_u] [name_f]Rowena[/name_f]!! 
I’ve known two girls named [name_f]Rowena[/name_f] who both went both Rowie. Though kids at school also called them Wena (weiner), but I don’t recommend that one!!