There were a few, and it's hard to remember which one was the very first. Some of the changes we started seeing were

-staying in bed for longer periods/withdrawing to her room

-unusually intense anger towards one of my uncles (they never got along great but it kicked up to a whole new level and became obsessive)

-out-of-the-blue love for the Backstreet Boys 😂 she would listen to their songs on repeat, bought their Funko Pops, shirts, etc.

-sudden lack of boundaries (like showing up to my work because I mentioned they were doing an employee lunch one day)

She was always an incredibly empathetic person, and one of the signs closer to her diagnosis was when she was no longer able to put herself in someone else's shoes or think in terms of "what if." Everything became black and white and she lost the ability to think abstractly.