DeNice and Beebi befriend Eleanor in gym class after watching Eleanor suffer as the target of Tina's bullying. They seem to mostly just hang out with each other, and aren't really a part of the main social group at school.
DeNice looks "too young to be in the tenth grade. She was small, and she wore her hair in two braided pigtails" (12.51), while Beebi, on the other hand, "was what Eleanor's mom would call a 'big girl.' Much bigger than Eleanor" (12.54). They both persist in striking up a friendship with Eleanor, persuading her to eat lunch with them and supporting her when Tina's gang is particularly cruel. Both girls are black, and because of their race, they're also outsiders, so they see a kindred spirit in Eleanor. Thank goodness, too, because they're her only allies besides Park.