I was reading about Myrtle and her death. I saw that she was a Ravenclaw and she died in the Gryffindor girls bathroom. Why was she in there?
It wasn’t a Gryffindor bathroom, it’s just a girls’ bathroom.
Myrtle haunted the girls’ bathroom on the first floor. There’s no indication at any point that the bathroom she’s in is intended only for Gryffindors - it seems to be open to members of any house.
“Oh no,’ said Hermione, stopping abruptly. ‘Turn back, turn back, I don’t want to talk to Moaning Myrtle –’
‘Who?’ said Harry, as they backtracked quickly. ‘She haunts the girls’ toilet on the first floor,’ said Hermione.
‘She haunts a toilet?”
- Harry Potter and the Chamber of Secrets, Chapter 8 (The Deathday Party)
There is a bit of inconsistency with the bathroom, but not regarding who can use it. The first time it’s mentioned, it’s described as being on the first floor, but later it’s said to be on the second.
“I suppose there’s always Moaning Myrtle,’ he said gloomily, referring to the ghost who haunted the girls’ toilets on the second floor.”
- Harry Potter and the Goblet of Fire, Chapter 22 (The Unexpected Task)
However, it’s consistently described as a girls’ bathroom, and never said to be House-specific.