"She out of her poverty put in all she had to live on" (v4). Like Jesus' listeners, we still are impressed by people who give huge, public gifts to charity or church. We all want to appear more righteous than we are, like the scribes who prayed long prayers, and the rich who gave out of their surplus. (Statistics show that the wealthy give away the least, proportionally, of their incomes). Jesus praised the widow, unnoticed by others, because she gave sacrificially and quietly.
The challenge of real faith is to give, pray, and help when no one is looking.