I am sorry that you have lost your mother. I know that is a grave loss for anyone who truly loves their parents and it is obvious that you loved her.
I want to help you with your thoughts concerning her. However, you must understand that I cannot declare someone else to be in heaven. I do not know the testimony of your mother as you do. I can only tell you what happens to those who pass away knowing Jesus Christ as their personal Saviour.
The Bible teaches that those who die in the Lord are asleep in Jesus (1 Thessalonians 4:13-15). But this does not mean that they are unconscious. Rather, it means that their condition is temporary--just like sleep. After a time, they will rise up from their sleep. When Jesus spoke of Lazarus, He said that his sickness was not unto death (John 11:4)--yet, Lazarus died. By not being "unto death," He meant that Lazarus would not remain dead. Then, when Jesus told His disciples that it was time to go to Lazarus, He said that He went to wake him out of sleep (John 11:11). But He had to explain to the disciples that Lazarus was dead (John 11:14). By waking him from sleep, He meant that He would raise Him from the dead.
However, being asleep in Jesus does not mean that we are unconscious in the grave. Paul was sure that to be absent from the body was to be present with the Lord (2 Corinthians 5:8). That is, he knew that as soon as his soul left his body, he would be with the Lord. In Philippians 1:21, Paul states, "For to me to live is Christ, and to die is gain." Certainly, it is not better to be lying in a grave unconscious than it is to have Christ living in you in this life. Two verses later he speaks of his "desire to depart, and to be with Christ; which is far better" (v.23). In other words, when he departed this life, he would immediately be with Christ. That is the hope of every Christian.
When Christ returns to earth to resurrect the dead in Christ, "even so them also which sleep in Jesus will God bring with him" (1 Thessalonians 4:14). You see, even though their bodies lie in the grave, the real person is with Jesus and will come back with Him to experience the resurrection of the body. Perhaps this explains Luke 15:10--"Likewise, I say unto you, there is joy in the presence of the angels of God over one sinner that repenteth." When a sinner repents, someone who is in the presence of the angels rejoices. Perhaps it is a loved one who has already gone home to heaven who is rejoicing.
One final word: do you also know Jesus Christ as your Saviour? We cannot enjoy eternity with our saved loved ones unless we also are saved and on our way to heaven. However, I can assure you that if you or anyone else in your family came to God, your loved ones in heaven would rejoice at the event. And, for those who know Christ, what a glorious time of rejoicing we will have when we all meet together in the clouds and in the air (1 Thessalonians 4:17)--forever with the Lord and forever with our loved ones. As the song says, What a day, glorious day, that will be!