Your question poses an age old question of faith. How can I be sure of God and God’s actions here and now, and in the world to come? .The short answer is that the will and grace of God is supreme and sure in our lives. The longer answer is that God in Christ is the ultimate authority in matters of sin and forgiveness, life and death, salvation. Not us, nor people, or any other creation of flesh and blood can determine ultimate matters of God’s grace and mercy .
Many times Christians can be far too quick to pass judgments and determinations on people they may not like or disagree with. That someone is beyond the pail, or power of God for salvation, all because we do not either like them, or do not think and feel they same way we do. None of us have the perfect knowledge and will of God or Christ to pass judgments on the eternal souls of other people. I always remind people of faith to be vary careful who or whom one may doubt their status with God. We all will be surprised once we get to the eternal place with the Lord, and see whom we will meet, and whom we will not. Such is the sovereign and perfect will of God and His Savior.
Being in a better place, Heaven, the afterlife, the time to come, life after physical death is still, and will always remain a matter of confession of Jesus Christ as Lord and Savior, confession of Sins, and seeking the healing of God, for we are all a broken and sinful people by nature. The salvation of God is universal, meant for all His creation. But it is not universalistic, meaning that all are saved by the simple virtue of being human or alive. Christ is still the only name that saves and enables salvation and eternal life.
Assuming as you said you never really got along, were estranged, or strained in relationship, these things happen in this life. But God and faith still calls us to pray, pray, and pray some more for those we may not always like and those whom we call an “enemy”. I would hope that no matter the nature of the relationship that you prayed for your mom, upheld her in prayer, and continued to do so, even if she rejected every attempt or effort to reconcile. At the end of the day, people die, some we liked, others we do not, some who broke our hearts, and some who rejected us or our attempts to reconcile. Your mother may have never found peace or blessings in this life, she may have carried a lot of pain or hurt in her life. Broken relationships are usually a result of some family based hurt or trauma in the past. But God was always there, God cares and the Good Lord will always, always bid His people to come home to Him. Let us all hope and pray, that your mom is now in a state of grace and she awaits you in His kingdom and at that time, we will be a family once more. In that is Hope and peace.