Why was Jenni Barber (Lisa) mostly absent for the third season?

Several years back (on the old IMDb message board) I wrote how I came to the conclusion that the third and ultimately final season of this version of The Electric Company was when the show officially jumped the shark:
https://moviechat.org/tt0995011/The-Electric-Company/58c879b1d1ea5c147070a466/Did-The-Electric-Company-jump-the-shark-in-the-3rdlast-season

The biggest question of all of this is why Jenni Barber, who played Lisa was for all intents and purposes no longer apart of the show? The show explained her not physically taking part in the storylines anymore but saying that she was away at science camp. But what was the behind the scenes reasoning for why Jenni couldn't take on a more active role like in the first two seasons?

Was it simply a scheduling conflict with her other commitments like her musical theatre work? I read that PBS Kids shows are usually produced much like British programming. Basically, they don't work on a regular schedule.

https://moviechat.org/tt0995011/The-Electric-Company/58c879b1d1ea5c147070a45f/Is-this-ending