Really my parents just made it up. My dad liked Rhiannon, but my mom did NOT want me named after that Fleetwood Mac song (though a good song!). My mom loved the name Rae, and she really liked Anna (pron. aw-na instead of ann-a) so they just comprimised with Reyanna (ray-AWN-uh). :) I say my name means "graceful sheep" or "graceful lamb", which is the meaning when you put Rae and Anna together.
There is a Turkish name: Reyhan, which means "sweet-smelling flower", and Reyanna is also a form of some Arabic word, but I don't remember. My friend from Saudi Arabia told me that.
But your friend's idea for a name looks like a form of Rhiannon, and you can follow the hyperlink for that one. :) Or it could be from the Greek rhaion, which means "more relaxed".