Tess Gander hails from issue number five of the DuckTales comic published under the Disney (not Gladstone) imprint.  The story is called "Down, But Not Out, in Duckburg."  There is no story code listed.   It was written by Marv Wolfman, drawn by Cosme Quartieri and Anibal Uzal, and colored by Gail Bailey.

Scrooge visits one of his paper-clip factories, which is also secretly the storage place for many of his jewels and gemstones.  He's in the middle of another battle with Flintheart Glomgold, who's taking away control of many of Scrooge's assets.  In the process of trying to thwart Glomgold, Scrooge is out in the rain too long and catches cold.  Huey, Dewey, Louie, Webby, Launchpad and Mrs. Beakley take him back to the factory, where they put him to bed in an old cot leftover from the Klondike days.

The caretaker of the factory and gem storage is an old, bearded duck named Gabby McDrake, who was a guide during some of Scrooge's Yukon expeditions.  He mentions how, back during the Gold Rush, Scrooge fell ill for 37 days, and he and a duck named Tess Gander nursed him back to health.  Gabby always sighs when mentioning her, and says, "What a beauty!"  It's obvious that Gabby carried a torch for Tess, but it is hinted that Scrooge liked her, too.  "Them sick days were the good ol' days for sure!" Gabby recalls.

Scrooge's fever soars until he is delirious.   Gabby tells the nephews and Mrs. Beakley that, "This is just like when he had that fever back in the Klondike!  Back then Tess  *sigh* an' me used his memories to snap him out of it."  The nephews help Scrooge to remember some of their previous adventures, dipping into Barks tales to tell about the golden fleece, the nugget boat and the Cura De Coco village.  This does the trick, and Scrooge suddenly snaps out of his delirium and is well enough to go beat Glomgold.  :-)

It's rather hard to see Tess in the picture above, so I enhanced the image a bit... 

I also enlarged, cleaned up and computer-colored the image...