Do you have a source from someone who isn't trying to sell me a book? I mean, she was world famous. She met millions of people and pretty much all of them say she was an amazing person.
I remember people were mad that she didn't make the effort to go to Princess Diana's funeral (they met several times and were friends) only for it to turn out that Mother Teresa died around the same day.
I never met mother Teresa, so I don't have a first hand opinion. But, "she was a jerk, according to my book - you should buy it" isn't a winning argument.