She’s Known as “The Listener”
Personal Head-canon: Guinan doesn’t appear in the later TNG movies because she left the Enterprise to save Ro Laren when the Dominion wiped out the Maquis. After that, Ro became her companion and they travel space and time in her TARDIS.
What, you think Guinan isn’t a Time Lord? Centuries old, looks human but isn’t, hangs out with random historical figures, unyielding hatred of the semi-mechanical race that wiped out her people? Come on!