Sorry for the tardy reply,
Pitch. Glad to see that
Galin has pitched in.
I was tracking down where I had read that Luthien was 'daughter of flower's. It is in the article on Luthien in
Tolkien Gateway, which unfortunately does not have a reference. However, the articles there on both
loth and
luth refer to the Tolkien reference Galin cites, from
Parma Aldalamberon XVII.
HoMe II also provides another interesting context. Luthien,
Man of Luthany is the name given to Aelfwine by the Elves, where Luthany is used for England. At this early date, only Tinuviel is used for Melian's daughter. (I think--it's been a few years since I read II.)
My naming of Rosie Cotton was not meant to imply that 'Cotton' was a floral name. My reference was to her first name, as the context suggested, and I used her full name only to grace her with her full identification.