From what I saw of her interviews and writings nothing she said is untrue. Your average American (or any westerner) would agree with most of what she says (even “conservative” Americans).
HOWEVER that does not mean that there aren’t people that are happy living the lifestyle she found and most Americans would find so oppressive. For some it is the best way to live for others it isn’t.
The book is a memoir, so of course it will be colored by her opinions and outlook of its author. That is what a memoir does! It isn’t supposed to be a scientific study of Satmar or any other community.
I think that the reason why people are so defensive is because they themselves are too insecure to just admit that what she says is true but NEVERTHELESS they feel that the good in the community outweighs the bad. As a general rule it doesn’t offend people who are secure in their beliefs when someone disagrees with them.