The content is only part of the equation on YT, thinking otherwise is deluded.
Many successful channels seem to see the same pattern, at least half the views, if not more, from old videos.
Sure it's possible that a fraction of her viewers got a bit tired of hearing maybe too much about her life than they'd like to hear.
But there are many factors at play regarding how YT promotes videos, most of which being completely opaque, and the way YT promotes your videos is what really makes the difference.
A sudden drop in frequency for new videos seems to be a clear factor. From what I've seen, it's more a change in frequency than the absolute number of new videos in a given time frame. If someone posts 1 new video per month with excellent regularity, they'll get better results than someone posting 1 video per week when they were posting 2 per week before, and so on.