There’s not much to it, but for the record:
1. I’ve looked at the video of that show and I can’t find the frame with the nipple.
2. I’ve never seen any other capture of the slip beyond this one collage which has been circulating for two decades.
It’s clear that Mariska was aware of a wardrobe problem and acted to remedy it, but it’s not clear that the slip was ever visible to the audience.
See further discussion of this in the comments.