IIRC, there's no way to get Grace to admit to her feelings until the end of the game, and no snogging either.
Or at least, if there is, I haven't found it yet.
Shame, but there ya go <img src="/ubbthreads/images/graemlins/biggrin.gif" alt="" />
Edit: The woman who voices Grace also voices Deionara, IIRC...