Why didn't Cassie sing in the "Prom Show" episode from Season 3

[TMC]

In "The Prom Show", the band for a high school prom that's being held at the restaurant doesn't show up, so the waitresses volunteer to sing instead.

At the beginning of the episode, they mention that Cassie has a cold, but nothing ever really develops out of this in the plot. It's just a random detail. Then later, Howard accidentally handcuffs Cassie to a pole in the kitchen and can't get them undone. While she's handcuffed, Dot, Amy, and Jan sing "Dancing in the Street." Immediately after the song is over, Cassie is freed, so it seems the only reason that she was handcuffed was to keep her from singing.

The ironic thing is that Ann Jillian actually had legitimate credibility as a singer elsewhere:


















Was Ann Jillian at the time, simply not well enough to sing, considering that she was undergoing chemotherapy after her double mastectomy? Or, did the producers simply think that it wouldn't be believable for someone with her voice to be waiting tables and not seeking stardom like Dot (who took the lead in the song)?