Heidi was a German waitress at the Double R Diner.
Heidi showed up to work late on February 24, 1989, claiming she could not get her car started, so Shelly Johnson finished the thought with "too busy jump-starting the old man, huh?" Heidi giggled as Bobby Briggs said "I thought you Germans were always on time." She giggled again, all the way back to the kitchen.
Roughly a month later, she came into work late again, seeing Bobby and Shelly teasing each other. Heidi claimed she could not get her car started, so Shelly finished the thought with "too busy jump-starting the old man again." She giggled all the way to the kitchen.
When asked on Twitter, Andrea Hays explained her absence between Pilot and Episode 29 as "I was, I'm just super shy and would hide out in the kitchen with Toad making ham sammachies. OR you just always came in on my day off??"
Heidi still worked at the diner twenty-five years later and had become acquainted with customer Miriam Sullivan, who one day left a tip that Heidi and Shelly agreed she could not afford. As a token of appreciation for Miriam, the waitresses planned to treat her to pie next time.