Yes the other, probably the most important factor, is bitrate which is almost the same across her newer and old videos (not always, but in the example mentioned above, they are).
I think she's either filming on an Iphone or just isn't compressing her videos/using a lossless encoder, thinking it's gonna look better.
I've watched the videos on a 4k display + zoomed in on them for better analysis and honestly the difference is so negligible that I can't even notice it.
Ok enough ranting.