Rowanne

The -anne at the end sounds a bit too "Frenchy" for me. Rowan is a strong English tree name, and if you're going to effeminate it, please end it with an -a. Rowana or Rowanna.

Looks tacky and forced. I prefer Rowan for boys anyways.

I like Rowan for a girl. I don't care for it on a boy. Rowen seems more masculine, and is better for a boy as it is masculine.
Rowanne or Rowenne is just too much, and it seems like somebody tried too hard to make it feminine. Rowan is feminine enough in my opinion, and -anne or -enne at the end of it is just extra.

To me, Rowan sounds feminine enough, so the -anne ending is rather ugly and superfluous.

I think this is a great name! Similar to `Roxanne`, but definitely prettier. This would be perfect if you wanted to name your daughter `Rowan` but want something more feminine. This is the name of a main character in the book `Criss Cross` by Lynne Rae Perkins.