I don't think I would make the connection with Diane.....
....Domina (also means lady), or does she have a mn or useable maiden name you prefer
I don't really get Diana from LaDonna unless you are just purely going for a short D____a name.
Donatella, Madonna, Belladonna (though this is a poisonous nightshade plant), Donella would seem to be closer.
Otherwise Donna means lady. LaDonna = the lady
Names with similar meanings: