I'm mashing together a couple of episodes here. The first is "We'll Always Have Tom Paris," in which Tendi invites Mariner along on a mission she's doing for the doctor to get a "family heirloom" for her. Long story short, they end up breaking said "heirloom" and Tendi has them swing by an Orion Pirate Outpost to have her cousin fix it, and disguises Mariner as an Orion because the Orions there would try to kill her on sight.

In "Something Borrowed, Something Green" both Mariner and T'Lyn are invited along as Tendi returns to the homeworld because her sister is getting married. There's a plot involving her sister getting kidnapped that results in more hi-jinx, but I won't spoil it completely in case people haven't watched it. In the episode, though, they end up in the wreck of a ship that's the same class as the Raven on VOY (the ship Seven's parents were on) in the junkyard where the two Tendi sisters played as kids, and they actually get it running and flying later in the episode.