I stated this as a question. If I absolutely "believe" my prayers can save my dead mother, I wouldn't have asked here for your or any other's opinions.
I have only understand the real meaning of "sorrow" after losing my mother. And including her in my prayers is a way of coping with it. Can I at least do that? Pray for the Lord to take care of my mother's soul?
And my point is that your initial question says very much about your beliefs. If you really knew the way of salvation you would never have asked a question like that. You would have
known that only the work of Christ makes the difference between heaven and hell for a sinner, not the work of the sinner - alive or dead - you would have
known that no amount of works or efforts of man can pay for his sins, but that the work of Christ alone was given as a ransom to that end. This is what the gospel is about. It would never had crossed your mind that your prayers for a dead person can affect its state as dead, let alone help "saving" that person.
This is a serious issue. Paul said that there are those that are zealous for God, but not according to knowledge, since they are ignorant about the righteousness of God, going about to establish their own righteousness, which they think will save them (Rom.10:1-4). Those who are yet ignorant about this are lost, according to Paul. So, either you are not saved and need to come to the knowledge of the truth, or you are saved, but something/someone has confused you and shaken your mind to begin to question the ground of salvation. Which one, I'm not sure. Are you by any chance a roman catholic?
Finally, I do not find it a sin to pray for a dead person (only to pray
to a dead person). But such prayers can only have a symbolical value, like battling sorrow etc, they can not affect the state of the dead. Their "fate" was finished when they walked the earth, as the scriptures I quoted in post #6 shows.