Lois Waller is a minor character in the Sweet Valley series of books.
Lois is the chubby daughter of the high school dietician, Mrs. Waller. She is often characterlized by her shaggy hair and large glasses. Jessica had always scorned Lois, even when they were children. However, it was her twin, Elizabeth who had always been willing to be more friendly towards the shy overweight Lois.
In the Sweet Valley Twins series, it was revealed that Lois and popular Janet Howell, were once best friends when they were children, but when she noticed boys, Janet had left Lois behind and became the snob she was.
In SVH#56, Lost at Sea, Jessica was teamed with Lois, Randy Mason, another geeky person who had gotten in trouble, thanks to Jessica wheedling him to tamper with her math grade; and Winston Egbert. Once again, Jessica had done everything to scorn Lois, Randy and Winston, whom she did not like, because they were not in the same caliber of popularity that she was.
For the most part, Lois is a very minor character.