Molly Weasley is considered a great mother for several reasons, both within the fictional world of the Harry Potter series and among readers.
Firstly, she is a very nurturing and caring figure, who takes on a motherly role not only with her own children, but with others as well. She welcomes Harry Potter into her home and treats him like one of her own, providing him with love, warmth, and a sense of belonging that he had never experienced before. This is demonstrated throughout the series, as she cooks for him, fusses over him when he is injured or upset, and defends him fiercely when he is threatened.
Secondly, Molly is incredibly protective of her children, and will go to great lengths to keep them safe. She fights in the Battle of Hogwarts alongside her family, and is willing to risk her own life to protect them. This protective instinct extends to those she considers part of her family as well, as seen when she fights Bellatrix Lestrange to save Ginny.
Thirdly, Molly is a strong, capable, and hardworking woman who manages to balance motherhood with her responsibilities as a member of the Order of the Phoenix. She runs a busy household, takes care of her children, and still finds time to contribute to the fight against Voldemort.
Overall, Molly Weasley is a great mother because of her unwavering love, protection, and nurturing qualities, which make her a warm, maternal figure who is beloved by both her children and readers of the Harry Potter series.