As far as I know, Mother Theresa did not actually evangelize. She did good works and merited much as a baptized Christian.
I have never heard of any proclamation she made of the faith. The most annoying line I hear attributed to her is “I’ve always said we should help a Hindu become a better Hindu, a Muslim become a better Muslim, a Catholic become a better Catholic.”. That hardly is going to get anyone in to the Church.
For a Muslim, to be a good Muslim is to listen to the Imam. For some Imam’s, to the best of their knowledge and understanding, the Quran says to kill the infidel and convert the world by the sword. So if we act according to Mother Theresa, there are some serious issues here.
People hated Christ. That certainly was not because he was sinful, yes?
Elements of truth can be found in other religions. But this is just a technicality unless one can say which is truth and which is falsehood, yes? So to say which is truth or falsehood, one must be Christian, i.e. Catholic. Otherwise, people will just be giving their best guess. As far as a non-Christian is concerned, their whole religion is true. Us saying that they have some truth in them only makes them think that they have no reason whatsoever to embrace Christianity. You know what they will say? You have some truths in Christianity too.
Well, think about it this way. If you were a Hindu who thought Christians were good intentioned but a mislead group of people, what part of Mother Theresa makes you change your mind?
If I was a Hindu with that view, I don’t see anything changing.
As far as I am aware, most of the saints were canonized (apart from Mother Theresa) for upholding teachings of Christ or proclaiming heroically. A person who just dies as a Christian does not relay anything unless they communicate they they are not afraid. But again we have WORDS. You do not canonize a Christian who died so that his family can get money from his life insurance, yes? So in this way, actions alone do not tell us much is my point.
So Mother Theresa helping the poor is GOOD works. That is something all Christians must try to do. But some have a greater calling. They are to try and feed the spiritual poverty i.e. evangelize.
What you see today is that people have made “feeding the poor” = “evangelizing”. That is not true. Feeding the poor gives an example for Christians and encouragement or reminder to do good works. But it does not give reason for one to become Christian.
So Mother Theresa in that sense is worthy of imitation as a Christian. But not in the sense of exclusively doing charity work but in terms of making sure one does engage in charity as well. Some others may have to do more according to their gifts.
Since this is getting way out of topic here, perhaps you can open a new thread on this very specific issues of Mother Theresa - Good works - evangelizing, I would love to join it. Just PM me the link after you open it
EDIT: Something that I have read not officially though is that people complained that Mother Theresa used most of her finances to fund actual missionary work. Since this is an accusation by non-Catholics, I feel that this may indeed be true. So in this case, it is possible that Mother Theresa did engage in a secretive movement to actually evangelize. Perhaps the Church does not want to emphasize this aspect of her at this time because that work is ongoing.
What I mean to say by this is that I cannot claim if she did or did not do missionary work at all. Maybe she indeed do a lot of it by supporting it with funds. But my point here is that the charity work, most usually associated with her, is not evangelizing work in and of itself.