Sweet Valley High: Rumors.

This is the 37th book in the series.

Susan likes Gordon. Something seems to be wrong with Susan's mother. Thre's going to be a ball for a bunch of ultra-rich snobs. Her father left long ago.

As of this volume, Jeffrey French is Elizabeth's boyfriend.

Lila Fowler doesn't like Susan so she starts a bunch of nasty rumors, not caring at all what effect it will have on Susan, such as losing her boyfriend.

Plot theme 2 is the girls and Steven concerned that their mother might be pregnant and doing everything can to see if that is true.

As rumors do the one about Susan's mother grows and becomes darker and nastier.

What happens afterwards is quite interesting. Susan has a major revelation about her mother. A guy that makes movies becomes an important character.Liz might leave the United States for a while.

A bigfoot eats Lila and dies of food poisoning.

Actually, no. I'd feel sorry for the Bigfoot.

Another book with an actual lesson in it. Don't start rumors. They can have really bad consequences for other people.