I would normally go for non repeat starting letters and say [name_f]Hosanna[/name_f] - [name_f]Hosanna[/name_f] [name_f]Dorothy[/name_f] is gorgeous and I love the nn [name_f]Honey[/name_f] (with [name_f]Annie[/name_f], [name_f]Nan[/name_f], [name_f]Sannie[/name_f] & [name_f]Sunny[/name_f] as other options). But I’m pretty compelled by Tori’s case for [name_f]Rosemary[/name_f] - and specifically [name_f]Rosemary[/name_f] [name_f]Dorothea[/name_f] (I would not do repeat Y endings in [name_f]Rosemary[/name_f] [name_f]Dorothy[/name_f] unless it sounds best with last name). [name_f]Rosemary[/name_f] as a first also gives you [name_f]Romy[/name_f] as a nn option besides the sweet Rose/Rosie.
As a wildcard: [name_f]Rosemary[/name_f] [name_f]Hannelore[/name_f] would be beautiful - gives you the nod to [name_f]Mary[/name_f], evokes [name_f]Hosanna[/name_f], and means you can use the nn [name_f]Honey[/name_f] (which you can of course for any name but makes stronger case for it). I love [name_f]Honey[/name_f]!
Good luck! 