I adore
Susanna (this spelling) enough to use.
Susannah is fine too for someone else; I just find the h weighs down the name somewhat. I do think
Sue or
Susie are avoidable although I'd probably call my
Susanna Susie (or even Susa or
Suzu). At least in the immediate family I would. I'd prefer that she be called
Susanna by everyone else.
Re:
Lily and
Susanna, I find the subtlety very charming and clever. Besides, many wouldn't figure it out anyway so you might as well use what you like.
"Darkness cannot drive out darkness; only light can do that. Hate cannot drive out hate; only love can do that." --
Martin Luther King, Jr.