I think this name is really cute. It makes me think of a really friendly witch, for some reason. The "my fanny" thing isn't really as big an issue in North
America, so no problems there - the pronunciation might bamboozle people, though, and they'd probably turn it into "my fan we".
Myfanwy EdwinaMyfanwy GretelMyfanwy MelindaMyfanwy NimueMyfanwy Gwen,
Myfanwy GuinevereMyfanwy ElvaMyfanwy Minerva