" The doorbell rang several times a day. As soon as it rang, Sirius's mother began to scream piercingly. Harry and others tried hard to eavesdrop on the visitors' conversation, but only a few seconds each time. After a few quick glances and a few scattered conversations, Mrs. Weasley called her back to work, and she didn't get much useful information at all. Snape came a few more times, but nothing happened. Harry was relieved that they had never met head-on. Harry also saw his Transfiguration teacher, Professor McGonagall, who looked very strange in Muggle clothes and coat. She also seemed to be very busy, coming and going in a hurry. "

——"Harry Potter and the Order of the Phoenix"

Judging from the fact that Professor McGonagall can enter and leave No. 12 Grimmauld Place, the core headquarters of the Order of the Phoenix, McGonagall can The professor is not only a member of the Order of the Phoenix, but may also be a core member. Judging from McGonagall's excited and very sad performance after hearing the news of James and Lily's murder in "The Philosopher's Stone", she should be an early member of the Order of the Phoenix

The example given by the tabby cat friend , I want to use two paragraphs from "The Prince" to explain (the second point is just below the example she gave, but unfortunately the tabby cat friend obviously thinks it is insignificant)

Dumbledore looked at him for a while , and then said: "Yes, I think Mr. Weasley and Miss Granger have proven themselves to be trustworthy. However, Harry, I ask that you do not allow them to tell anyone about these things again. If the news gets out, let It would be bad if people knew how much of Voldemort's secrets I knew or perceived."?

"I can't tell you, Professor." He had anticipated this question and had already thought of his answer. It was here, in this room, that Dumbledore had told him that he could only tell Ron and Hermione what they had been through.

In fact, in "The Hallows", Lupine also wanted to know the principal's plan but was rejected by Harry, but I don't think the tabby cat friends would say that Lupine was not a member of the Order of the Phoenix.