She took money from some despicable characters. She let people in her care suffer "to reach God" but had the best medical care for herself, when she fell sick. Her organization did not keep good records of financial transactions or pay correct taxes. That is just what I can remember. You can Google, lots of good sources are around.

She is not a person to look up to. Organized religion disappoints, 99 times out of 100

Some light reading. Miss the Hitch.

https://en.wikipedia.org/wiki/The_Missionary_Position:_Mothe...

She was far more interested in converting[1] souls to the light of Jesus Christ than she was in helping people with their problems in this world.

She was pretty good at convincing people that she was predominantly doing the latter, though.

[1] With allegations of unethical forced deathbed conversions.

among other things she believed sick people should feel pain because it came from god and withheld painkillers from them

The linked Wikipedia article about her links to a page full of criticisms: https://en.wikipedia.org/wiki/Criticism_of_Mother_Teresa

“With or without religion, good people can behave well and bad people can do evil; but for good people to do evil - that takes religion.”

― Steven Weinberg

First result in Google - https://en.wikipedia.org/wiki/Criticism_of_Mother_Teresa

Maybe: https://en.m.wikipedia.org/wiki/Criticism_of_Mother_Teresa