She mentioned earlier that she had been struggling with muscle pains but eager to return to working on the fediverse, so it seems like it might be physical health issues rather than burn-out.
No matter what it is it's normal that people's engagement in largely unpaid projects fluctuate over time. That said I hope we'll get to enjoy the product of her hard work, and more importantly of course that she is getting better and is distracted by fun rather than awful things.