Ignore the crap about fructose, it’s a waste of time to explain and ultimately not nearly as relevant as the fact that she’s really not getting that many micronutrients per calorie.
Just compare the micronutrient per calorie data of any fruit (even the really good stuff like avocadoes) to just about any green vegetable out there. Just look at a few major nutrients she might be familiar with – calcium, magnesium, iron, vitamin D – and show her that fruit alone is inadequate just for those basics.
Whatever you do, do not jam the ‘you have to eat meat’ thing down her throat. Most people do not respond to that, because it might represent a radical attack on her assumptions, which usually causes people to ignore you and avoid you in the future. (I say this with the assumption that she has some strongly vegetarian-vegan leanings, correct me if I’m wrong)
It’s like when you’re hanging out at home, or at a college campus, or some public event, and someone tries to do a full-court press to convert you to some religion or philosophy that is not part of your upbringing.
They are going to seem annoying, and you’re generally going to reject them outright.
Instead, consider convincing her of a very minor flaw in her current dietary approach. Once you convince her of a minor flaw in a way that works with her existing assumptions, she will be much more amenable to considering more significant changes to how she views food.