This is book number 3 in the The Baby-Sitters Club Graphix series.
When The Baby-sitters Club gets into a huge fight, Mary Anne is left to her own devices. She has to eat alone in the school cafeteria, figure out how to make new friends, and deal with her overprotective father. But the worst happens when she finds herself in a baby-sitting emergency and can't turn to her friends for help. Will Mary Anne solve her problems and save The Baby-sitters Club from falling apart?