I read this when I was younger. This princess name quen I think steps througfh this magic mirror or magic fountain or something and meets this guy who is an apprentice and they fall in love.
The cover of the book had her on the railing of some stars and she was in a green dress.
Any info would be appreciated! Thanks!

I think it's "Mordant's Need: The Mirror of Her Dreams."
I'm not quite sure, but I read a story of a girl who was always looking at herself in the mirror to ensure she existed. Then she looked in a mirror, and saw a man who claimed he was an apprentice or "Apt."

Thanks
But its not it.