[Nyororin]

Pretty much what MMM said. You can't write your friend's name in Japanese... It would cease to be her name altogether. Japanese has a different sound set than English, so even if you wrote something that sounded similar, it would only sound similar and not be that name.

If you want a tattoo of something that sounds kind of like your friend's name, go for it, I suppose. But it will never mean her name, even to native speakers.