When Transfiguring and head of Gryffindor House Minerva McGonagall learn about Remus Lupin, she didn't see him as monster. No she saw a scared boy. He was smart, and brave. And she made her duty to make sure that he was welcomed at Hogwarts. That's why she study and train to be come a animagus.
Yes she new it was kind of illegal but she didn't want Remus to be by himself in the dark all alone. She didn't know how to take the pain away. But she knew that being not alone helped than being alone. Plus being amazing at transfiguration she saw it as a cat. She didn't mind through, she always liked cats.
She didn't tell anyone else about this but Dumbledore figured it out. He was after all the headmaster. And I guess her sneaking into the library didn't go unnoticed. She just wanted to make sure everything was ready.
She even went to the secret passage way and charmed it to make sure that Remus would be safe from others. She made a bad, and blankets to make sure he was warm. Through she couldn't do much she was glad to help either way.
She was proud when he got into Gryffindor and saw quickly he made friends. But he was well nervous about it and she didn't blame him. She knew how cruel kids could be. She saw bullying and even try to put a stop to it. She hoped that young Potter, Black and Pettigrew will treat Remus with respect.
On the night of full room she turned into the cat and sneaked into the tree to the secret passage that Remus was in. He wasn't himself, he already changed into werewolf and was whimpering.
"Remus" she said in her mind and looked at him. He stop whimpering and cocked his head looking at the strange cat who was staring at him.
"You are safe" she whispered in her mind well to him. She looked at him with kind eyes and he seemed to understand. He laid down looking at her in wonder.
She walked up to him and laid next to him on the floor and watched as he fell asleep. She said with him his first night at hogwarts. She knew it wouldn't be easy but she would stay with him.. untill she figured out that his friends found out. They wanted to him. And she knew he was loved and he found a group..not only friends but family.
Nobody notice through as she stood in watch just in case.
For Remus wasn't a monster to her. He was almost like a son.