So your mum would approve of Siddanee? ;oP J/K!
Siddalee doesn't really do anything for me, either, but there are a lot of Southern US names I don't really care for (
Darby,
Darcy,
Wade Hampton, etc.). Funnily enough, I do like the sound; I just think the spelling is cumbersome. Perhaps Sidley would be more up my alley; I dunno. :o)
As for mn suggestions: Perhaps Siddalee
Dahlia (now THAT sounds Southern!) or Siddalee
Rhoda. Meh. I can't seem to come up with something that just pops, KWIM? Maybe Siddalee
Cassia?