Only God knows.
Ok, having got that out of the way, Internet Monk has an excellent post reflecting on how God can seem distant sometimes. In that post, he references a review of the new book revealing Mother Teresa's own spiritual troubles.
These letters are highly personal, and selected from times of confession and vulnerability. So we can't form an opinion from them.
But they can serve as an example for when we "Examine yourselves, whether ye be in the faith" (2 Corinthians 13:5a). If someone I knew, claiming to be a Christian, said these things to me, what would I think?
She says some disconcerting things, "I spoke as if my very heart was in love with God — tender, personal love," she remarks to an adviser. "If you were [there], you would have said, 'What hypocrisy.'" She claimed to have heard Jesus talking to her.
The question is, did she do what she did out of gratitude for what God had done for her? Or did she do what she did in order to try to earn God's favor (or some burden of debt)?
A similar question is, why does the world respect her? Because of her dedication to God? Or because she was "better" than anyone else at doing good works?
What is the example of her life? Is she someone to idolize? (while seeing her standard as impossible to reach, so we don't even try?)