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Mrs. Weasley is the biggest mother figure in the Harry Potter series. As the mother to Ron and the whole Weasley clan, she also eagerly welcomes Harry and Hermione into the fold. She tells Sirius point blank that Harry is as good as another son to her. The one problem with Mrs. Weasley's extreme motherliness is that she can also be smothering in her affection. Her overprotectiveness ranges from funny (she's constantly harassing her oldest son, Bill, to get a haircut) to deadly serious.
Mrs. Weasley is dead set against Harry, Ron, and Hermione participating too much in Order business, and she frequently fights with Sirius on the subject. Emotions run high during these fights, and she sometimes says almost unforgivable things. For example, she bursts out, "the thing is, it's been rather difficult for you to look after [Harry] when you've been locked up in Azkaban [prison], hasn't it?" (5.126). It's not exactly fair for Mrs. Weasley to throw Sirius's long prison term – for a crime he didn't commit, no less – in his face. These kinds of comments contribute to Sirius's overall bitterness and recklessness by the end of Book 5. Her overprotectiveness also riles Harry, who already feels left out of the decisions being made about his own life. She even goes so far as to suggest that Harry, Ron, and Hermione drop the D.A. because they will get in trouble with Professor Umbridge and the Ministry – trouble that, in fact, Harry desperately wants to provoke.
So, Mrs. Weasley's motherliness has a hard, somewhat cruel edge at times in Order of the Phoenix. But we also get more insight into why she is so intent on keeping Harry, Ron, Ginny, and Hermione out of danger, even when they don't want to be protected. When Mrs. Weasley is helping to clean up Number Twelve, Grimmauld Place at the end of the summer, she stumbles on a Boggart. A Boggart is a magical creature that can transform into whatever its victim most fears. As Mrs. Weasley tries to fight the Boggart, she gets overwhelmed by what it is showing her: the dead bodies of her whole family, one after another. Nearly the whole Weasley family is in the Order of the Phoenix, and with war against Voldemort coming, it seems inevitable that she will lose some of them.
Mrs. Weasley is intensely overprotective in Book 5, but we can also excuse her because she is living in fear of the future every minute of every day. No wonder she's a little tense: Mrs. Weasley's immense love for her family also means that she has a lot to worry about now that Voldemort is back.