I'm really not sure about the timeline with this, but the whole Alex Day thing caused a huge change in Carrie, and quite rightly so. What he did was awful, and she ended up being at the centre of this massive drama involving her boyfriend (at the time) being accused of sexual assault, statutory rape, and sexual coercion. Carrie had to find out that her boyfriend was not only cheating on her, but was being accused of being a sexual predator, all in the public eye of the huge YouTube community at the time. She did not handle this well at all in her online response, but there's no denying that's a huge trauma to deal with.
I also noticed a change when Alex released his book a few years ago. She spoke about this at the time, and how she's much more guarded with boundaries and things, which is possibly true from her perspective, but I think to a lot of people, the. change has been shown in a lot of hostility, attitude and bitterness from Carrie.