If you look at her posts, they were slowing down well before she left. She only made 31 posts between the 1st of January, and 14th of March, which was her last post.
She only made 32 in December, which isn't much for her either.
She mentioned having a knee problem, and was going to the gym every day because of it, so it doesnt sound like she was having any life-threatening health issues.
It really looks to me, that she's either just drifted away, or is dealing with something in her real life.