I don't know why you feel so strongly about this subject that you return to it four days later, but she is not an objective expert. She sounds like yet another low carb high fat preacher that wants to sell books, and she makes a flippant remark about how you emit methane after eating beans while "the vegans are blaming the cows". Oh, and she seems to eat plenty of fiber herself:

> I eat fruit most days, but not too much and because I like it, not because I think it is good for me. I eat a lot of vegetables/salads – locally grown/in season wherever possible. [...]. I do eat starchy carbs – just not daily. I enjoy porridge (plain oats and whole milk) – especially in the winter. I like brown rice and (veggie) curries/chilli.

https://rationalwiki.org/wiki/Zo%C3%AB_Harcombe

Even if you don't believe in or care about any health benefits fiber may have, two benefits are immediate after eating them: they fill you up and make you feel full without containing any energy which helps mediate calorie consumption, and they make bowel movements easier, at least if you drink enough water. I believe most people would feel better if they ate more fiber instead of red meat and fries.