From what it sounds like, a second miracle has been recognized for Mother Theresa, who when canonized will most likely be the best answer for the question of who was the worst saint. Criticism of Mother Teresa - Wikipedia
A vile, disgusting human being, dressing up her views through organized religion into something that other people saw as positive because of her “faith”, which her posthumously revealed writings suggest she really didn’t have any of.
St Olga
This question makes me think of the famous Pope Wormer I:
“Cardinal Greg… Who is the worst saint in the Catholic Canon?”
“That would be hard to say, Your Holiness. They’re each outstanding in their own way.” 
Ah, yes, Theresa, whose terrible crime was that she didn’t single-handedly eradicate poverty in Calcutta. Let’s see you do any better with the resources she had.
You really should check out what Christopher Hitchens had to say about this dreadful old poseur before defending her. Mother Theresa wasn’t about the lessening of poverty and disease, she was about their perpetuation for her own glorification.
A link to the column in question.
In post #2, blue infinity brought up a quote about St. Olga:
Where is this quote from?
Is Archie Manning Catholic?
It’s been debated, leading to the conclusion that we can’t conclude anything.
From the Wikipedia article.
Not the poster, but I was curious too. The Wikipedia article on Olga of Kiev credits something called the Russian Primary Chronicle, which a separate Wikipedia article indicates is a surviving medieval text.
Uh…scooped.
I realize that it’s the classic Christian ‘get of jail/hell free card’, but Olga’s bad behavior was apparently from long before she converted.
Ideally, one would like to raise all of Calcutta, or indeed all of the world, to a middle-class life or better. Of course, that’s impossible. One must choose between giving a lot of help to a few people, or giving a little help to a lot of people. Mother Theresa chose to give help to as many people as possible, which meant that the amount of help for any given person was extremely small. That doesn’t mean she hurt anyone, though.
A lot of people love to try and tear down Mother Teresa, but I offer to you Junipero Sera. Noted enslaver and enabler of exterminators of California’s native population.
No, no; she had the temerity to attempt to convert the poor to Catholicism. That’s a path leading right to Hell.
Gregory VII did push through some church reforms but his main claim to fame was promoting the supremacy of papal power over secular rulers. While that might have been a popular cause within the church, I personally don’t see it as an accomplishment which deserves canonization.
Secretly baptising dying patients with no regard to their professed religion isn’'t conversion, it’s abusing the defenseless and typical of this vainglorious old crackpot.
The problem was that when she had plenty of money flowing in to help people, she didn’t spend it on alleviating people’s suffering. She wanted them to suffer, as she thought they would be closer to Christ. All the money that people donated to her went not to feed people, but to proselytize. So she’s a wonderful person from the view of the Catholic Church, wanting to preach to the utterly destitute and give them a place in eternal life, but from the viewpoint of someone who thinks churches are best used as a means of providing a community spirit so that people will help each other out with their worldly problems, something that most of the people who heard about her assumed that she was helping bring about by connecting donors to people to need, she was an absolutely terrible person.
I do have to say though that the death bed forced conversions I have absolutely no problem with, assuming that the energy and resources needed to do so were sufficiently minor. If the person who was forced to convert thought that the baptism would help, they would want it. If they didn’t think it would help, it was a silly ritual that at least made the ministers feel better and didn’t affect them in any other way and they could go on practicing whatever they felt like. Unless you follow a polytheist religion and think that the Catholics were stealing souls from some other God, you shouldn’t have a problem with it.