Later in the year, McGonagall duelled with Death Eater Alecto Carrow during the Battle in the Astronomy Tower and later learned of Snape's murder of Dumbledore. McGonagall was initially appointed as Headmistress, but was demoted after Voldemort took control of the school and placed Snape as Headmaster.
Professor McGonagall did not know. It took her by surprise just as it took Harry by surprise. Dumbledore played his cards very close to his chest and was a true believer in the tactic that “if you want to keep a secret: tell no one!”
Most of the teaching staff learnt at the end of Half-Blood Prince: Lupin, Tonks, Professor McGonagall and Madam Pomfrey were told that Snape killed Dumbledore at the end of Half-Blood Prince. Hermione and the Weasleys were in the ward, so learnt at the same time.
Professor McGonagall knew that Snape was working with Dumbledore. Everyone in the Order did, which is why Snape was actually let into Order meetings - if they didn't know, they'd likely have tried to not let him it. However, she didn't know that Dumbledore and Snape planned Dumbledore's death.
Actually every one were very much aware about the plan to keep Harry safe, but no one really knew the extent to which Snape is on that plan. So, Dumbledore kept it secret because he thought it is essential for the safety of Harry Potter.
McGonagall was initially appointed as Headmistress, but was demoted after Voldemort took control of the school and placed Snape as Headmaster.
Similarly to Harry, Snape's patronus represents a person. In the memories he gives Harry before his death, Snape shows Dumbledore his patronus, using the form to prove his love of Lily Potter, Harry's mother. This indicates that Lily also had a doe patronus.
It's a word that gained so much more clarity and tragedy after Harry Potter and the Deathly Hallows revealed that the nefarious Professor Severus Snape was actually serving a nobler cause: protecting Harry from Voldemort out of love for Snape's childhood friend Lily Evans.
Pursuing, McGonagall screams, "Coward!" Uncloaked, Harry and Luna rush inside, startling the other professors. Snape has leaped out the window. Harry thinks he must be dead, but McGonagall bitterly comments that, unlike Dumbledore, Snape had a wand and has learned a few tricks from "You-Know-Who".
Verdict: Snape Is the Stronger Wizard
McGonagall is surprisingly skilled in the Dark Arts but not on the same level as Snape. She's also most likely incapable of casting the Killing Curse, which puts her at a disadvantage.
“You disgust me,” said Dumbledore, and Harry had never heard so much contempt in his voice. Snape seemed to shrink a little, “You do not care, then, about the deaths of her husband and child? They can die, as long as you have what you want?” Snape said nothing, but merely looked up at Dumbledore.
Draco had several reasons for lying to Bellatrix, including the fact that he was never a bad person. Moreover, he no longer found working for the Dark Lord appealing and hated how Voldemort treated his family. He did not intend to harm anyone and believed Harry was the only person capable of defeating Voldemort.
Snape was then chased by McGonagall, Sprout, and Flitwick into a nearby classroom, jumped through a window and flew away, a skill he presumably learnt from Lord Voldemort. Minerva contemptuously called Snape a "coward".
Professor McGonagall is a Death Eater
According to the theory, McGonagall's seeming disregard for Harry Potter's safety, her talent for transfiguration, and and her stoic nature all point to the fact that she was a Death Eater.
Snape took the fall instead at Dumbledore's insistence. But, that's not all. Dumbledore was also aware that he wouldn't be alive for long because he had been cursed by the Horcrux ring. Instead of suffering a painful death, he urged Snape to end his misery.
So Snape was cruel, biased towards his house, and downright rude to his students: this we can't deny. Calling poor Hermione an 'insufferable know-it-all', for example, was pretty terrible.
McGonagall followed up Harry's action by using the Imperius Curse on Amycus before tying him up with a net, rendering him useless during the Battle of Hogwarts.
Weaknesses. McGonagall is never portrayed as having any particular weaknesses. Her stern facade likely prevents anyone from getting close to her emotionally, with the possible exception of Dumbledore. We are led to believe that she prefers her solitude.
Harry also happened to be Snape's least favorite student.
The first thing Snape asks Harry is "Potter! What would I get if I added powdered root of asphodel to an infusion of wormwood?" According to Victorian Flower Language, asphodel is a type of lily meaning 'My regrets follow you to the grave' and wormwood means 'absence' and also typically symbolised bitter sorrow.
It is without a doubt Draco Malfoy, it's very obvious throughout the series how favourably he treats Draco, there are many different factors for this, as we know Both Student and teacher are in we're in Slytherin and so this is a reason for the connection.
Now, as firmly established, Snape was not the greatest fan of Harry, but that didn't mean that he ever stopped loving Lily. Dumbledore was surprised that Snape seemed to care for the boy. With a swish of his wand, Snape conjured up a Patronus – Lily's Patronus, a doe. 'Always,' he said.