Absolutely!! Grace (Grackle) is a great example of this!
When it comes to Holly's hair, her texture could be caused by a few things, though:
A) Genetics, some people have "fluffier" hair than others, mostly caused by thinner hair strands.
B) She might be over-washing her hair, since she exercises every day?
C) She's not using a conditioner or hair oil, or any silicones (I think). Some silicones sits on top of the hair strands and kind of form an armour that protects against damage like heat and friction. Silicones doesn't work for everyone, and that's okay.
D) Like others have said, putting it in a bun or a pony tail, is not a great idea. Why doesn't she ever braid it instead?
But it also makes sense that it's her diet (lack of energy, protein, fats, minerals, vitamins) that's causing alot of the damage. Hair grows slowly, so it might take months or years before you see the true effects of a malnutrition. I've personally experienced hair loss a few months after a really stressfull or depressing period of my life, especially if I didn't eat properly during that time. It's strange how it doesn't happen straight away.. I'm not sure if Holly's hair line is receding, because from earlier videos it looks like she's always had that hair line? But I'm definitely not 100% sure.
HOLLY, GO SEE YOUR DOCTOR AND GET A BLOOD TEST FOR MINERAL AND VITAMIN DEFICIENCIES.