When Lazarus died, many people were mourning. Once Jesus came to the area, Martha went to Jesus to talk to Jesus.
Martha stated that if Jesus was there, then Lazarus wouldn't be dead (11:21). She made the comment likely because she is aware of Jesus healing a lot of people in His ministry. Her comment also implies that she wanted Jesus to come earlier to save Lazarus. At the same time, Martha knows that whatever Jesus asks of God, God will give to Jesus (11:22). She likely knew that Jesus was significant enough to have a link with God, even when Jesus came after Lazarus died.
In response to Martha's comment, Jesus told Martha that Lazarus will rise again (11:23). Martha knew that Lazarus will rise again at the last day. That is true ... but Jesus had another sense when He said that Lazarus will rise again.