The Marauders were definitely McGonagall's favorite students, especially James. Dude may have been a bit arrogant, but he was brilliant at the two things McGonagall loved most - Quidditch and Transfiguration.
And then Lily Evans joins for a serious discussion (as serious as you can get with a half-drunk Sirius) and everyone is very surprised, except for Remus (and probably James) who also joins, because "And the sexist publicity, don't forget it, Padfoot"
In Lily's letter to Sirius, she mentions how Harry nearly killed the cat with the toy broom that Sirius got him. Well, what if that's the reason that Crookshanks has a squashed head and a flat face? <<<<< BEST HEADCANON EVER!