Mitzi first appears in the film at her and Blitzen's home with their newly born son whom Blitzen suggests they name Rudolph to which Mizi considers a wonderful name. Rudolph begins to take his first steps, but tumbles into a hay bale. Mitzi and Blitzen rush over to see if he's okay. Rudolph emerges from the hay bale unharmed, but when he lets out a sneeze, his nose lights up red, to the shock of his parents with Mitzi saying bless you.
The next day, Mitzi and Blitzen take Rudolph a tour of Santa's Village, where they meet with Blitzen's three brothers Comet, Cupid and Dasher. Worried about what they would think of Rudolph's nose, Blitzen tries to hide his son from his brothers to which Mitzi questions him if he's embarrassed by his own son. Blitzen let's Rudolph go, but after been tickled by Cupid, his nose lights up in front of the rest of the villagers. Mitzi and Blitzen take Rudolph away with Blitzen claiming to the villagers that Rudolph has alleges. Mitzi and Blitzen then sing "What About His Nose", but when Comet, Cupid, Dasher and the villagers join in and start laughing at Rudolph, the two quickly take Rudolph away. The family then go to Santa's workshop where they witness Santa face against Stormella, The Evil Ice Queen who wants to know which elf destroyed her ice garden (revealing an elf's hat as evidence). It is revealed that Boone and Doggle were responsible, but Santa refuses to hand them over to Stormella who in retaliation, closes her bridge off to the public and threatens to cast a storm to put Santa out of business if anyone crosses it.
A year later on Christmas Eve, Mitzi and Rudolph along with the other villagers watch Blitzen and the other Flyers guide Santa's sleigh into the night for his deliveries.
A few years later, Mitzi and Blitzen attend The Junior Reindeer Games to watch a now teenage Rudolph take part in The Sleigh Race. They are at first happy when he wins the race, but are then disappointed when he is disqualified for supposedly using his nose's light to cheat and caused his cousin Arrow to crash with the other racers (when actually it was Arrow's taunting that caused Rudolph's nose to lift up). After returning home, Mitzi and Blitzen find a note from Rudolph and learn that he has ran away. The two along with the mother and father of Rudolph's friend Zoey (who had left to look for Rudolph) come to Santa for help to find the two, to which he sends Boone and Doggle.
On Christmas Eve, Mitzi, Blitzen and the other villagers are told by Santa that he has to cancel his Christmas Eve launch (as Stormella had cast her storm due to Zoey crossing the bridge). Just then an elf points out a light outside Santa's house to which everyone goes outside and sees that it is Rudolph along with Zoey, Boone, Doggle and Rudolph's friends Slyly and Leonard. Mitzi and Blitzen greet their son and witness him being asked by Santa to use his nose's light to guide his sleigh through the storm to which Rudolph agrees.
Mitzi is last seen the next morning on Christmas Day singing Rudolph the Red-Nosed Reindeer with the other villagers as Rudolph, Santa and the Flyers return.