Just like lots of other teen horse "experts". She has a lot of big opinions but does not have the years of experience, mistakes, and humbling situations that older riders/trainers have had. She's just using a very public forum to voice those opinions as loudly as possible.
Many young people like to feel like they are looked up to, or authoritative about something. It gives them a sense of control and power, which is quite addictive to someone who really does not have any in their lives. Here they are, not even in college, but they are giving advice to thousands on a world-wide scale! Whether or not it is GOOD advice remains to be seen.
Time and experience humbles many an opinionated person!