She just has really fine hair. From what I've seen of her kid pics I'm pretty sure she straightens it which makes it look thinner. Unfortunately as I have experienced you can't magically make it thick and full. I think her hair is actually in some of it's best condition, not dyed, not frizzy or dry looking. I also have the same thing on my hair line, it's a patch where the hair grows back and blends in well with the scalp colour wise so it looks balding at some angles. I can guarantee her hair will never look thick without the styling of a pro. This is all coming from someone who has almost identical hair and has tried everything before accepting that it's just how my hair is.
I honestly think if she didn't waste so much time editing her pictures she could post more and have a more organic insta it would balance out potential loses of followers to new ones. Plus it would be so much better for her mental health.
Sounds odd but I stopped watching when she started constantly throwing on self tanner. I'm super pale so her beauty stuff was great to find styles and colour to suit me and her fx were fun as a beginner but now I'm taking things more seriously she looks more amateurish and with the whole adpocalypse thing I don't think her heart is in it anymore hence all the meme and trend videos. Also what is with these drugstore fx videos? Even she said it's cheaper to buy the proper stuff and it'll look way better.