Harry Potter Fan Theory: Why Professor McGonagall Was Secretly A Terrible Person
Why did she ignore the abusive Dursleys?
Putting aside the fact that she's horribly irresponsible in putting Harry on the Quidditch team and generally isn't a very good member of the Order Of The Phoenix in any tangible sort of way, there's now a suggestion that she was willfully part of Dumbledore's ignorance to Harry's abuse at the hands of the Dursleys.
As one eagle-eyed Reddit poster has suggested, when Dumbledore is accused of treating Harry awfully by letting him rot in Privet Drive with abusive family members who resent him for his magical genetics he's not the only one allowing it to happen. Because McGonagall knows all about some of Harry's torment and does precisely nothing to help him.
She knows where he is as she's there when he's dropped off by Hagrid and despite apparently caring for him she never writes nor visits (not that that would be particularly allowed, but she's an animagus and would be the most well-equipped witch to visit under-the-radar). Had she done so and perhaps showed the Dursleys that the Wizarding World was watching their treatment of Harry, he might not have had such a miserable upbringing.
But by the look of it, McGonagall merely put Harry completely out of her mind from the second she watched him being left with his abusive, magic-hating family. And it's not like she was unaware of his treatment either.
When Harry gets his letter from Hogwarts, there's a big suggestion that McGonagall was well aware that he was being forced to live like an unpaid servant. After all, the letter comes addressed to Harry's room under the stairs and it was sent not by Dumbledore, but by McGonagall. In other words, she knew he was being forced to sleep in a cupboard - something you'd think she might have concerns about.
So did she really know? Could this be another step in the idea that McGonagall was actually a sleeper agent for Voldemort? The evidence is certainly adding up. Either that, or she was just as negligent as Dumbledore...