Yesterday on the Babylon 5 subreddit, a clip was posted which appears to show Pat Tallman as a background character in The Undiscovered Country. If so, that would be her first known appearance in Star Trek, after which she appeared as another nine* characters in addition to stunt doubling eighteen times for fourteen actresses according to Memory Alpha, which currently doesn't include her apparent appearance in Star Trek VI. *Her two appearances as an Enterprise-D officer and possibly also as a Defiant weapons officer could be as the same character.
And unsurprisingly, sporting the same cut she had in the early '90s for her first TNG spot and the Night of the Living Dead remake. MemoryAlpha doesn't seem to list that "character" at all, so I guess they just missed it. You should go rectify.
Here are a couple of screencaps of the 4K blu-ray where you can see her face. I checked the old SE DVD with the taller aspect ratio, but all the extra material in that shot was extending from the bottom of the frame, so there isn't any more useful information. MA editors, feel free to use these.