According to the Holy Qur’an, are the good deeds of people like Mother Teresa lost?

No. The verses about lost works refer to nations that as a whole strive only for worldly gain and forget God in the process. God does not overlook the good a person does out of a compassionate heart.

The verses in the chapter Al-Kahf speak of people whose effort is lost because it is wholly absorbed in the pursuit of worldly things, while they think they are doing good. They do not describe individual kind people, but the direction of whole nations.

What is meant are societies that have made great advances in science, technology and industry, yet as a whole use this power only for material gain. With their inventions they make no attempt to please God. Many of the burdens that poorer countries carry are linked to this race for industry and trade.

Even in such societies there are individuals who serve humanity, like small drops of water here and there. Their service is recognised. But they do not change the direction of their whole nation, and so the statement about the whole remains true.

With people like Mother Teresa something further comes in. Their service often springs from a natural tenderness of heart. Some people cannot bear the suffering around them. It torments them so much that they find no rest until they have done something about it. This kindness is genuine.

The second verse above makes clear that God sees even the smallest good. And the third shows that God's reward is not tied to one group. No one need fear that good done sincerely simply vanishes before God.