I've read that she denies ever being in TNG, though, I believe, she was in two episodes (though I can't remember which ones).
She also appeared in 'Darmok'.
Ashley Judd played the character of Robin Lefler in two episodes:
The character's role in Darmok is not significant (she is part of La Forge's team working on the transporter), but plays a major role in The Game.
With respect to denying her appearance, my guess is that you are referring to an apparent mention by Judd on Letterman that she would reprise the role in Star Trek Nemesis (there are many references to this, but I can't find anything authoritative - it was 2002). This did not turn out to be the case, and was later denied by Judd's spokesperson (I can't find any authoritative source for this, either).
She certainly doesn't deny being in Star Trek as this video shows;
Wesley Crusher's part in Nemesis was certainly cut; it's possible that Judd was cut too, or that Lefler was in an early script but never filmed. There doesn't appear to be any definitive evidence either way.