I suspect that your daughter’s friend is merely ineffective at expressing her personal choice.
There are some individuals who go to the extreme of eating nothing that has not fallen naturally from the plant, rather than harvest the plant itself (they eat only fallen fruits and grains, etc). I don’t remember the term, but as I’m sure you can imagine, there are not many who are capable of following such incredibly strict guidelines.
Most vegetarians who choose to avoid eating meat as a moral decision do so because animals are capable of suffering and of perceiving pain, which plants are widely accepted as being unable to do. But you should avoid making broad generalizations about a varied group of people who make a similar life choice based on a great many variables. Some people chose not to eat meat because they feel they are physically healthier that way. Some people (myself included) choose not to eat meat because they do not approve of modern agricultural practices and prefer not to eat meat that is full of hormones and antibiotics and is contaminated with (literal) shit because of slaughter and handling techniques.
I may be mistaken, but your tone seems to be quite scathing. Rather than denigrating a young person who has actually changed her behavior in an effort to improve her world, perhaps you could congratulate her for following her convictions, regardless of whether or not you agree with her.