I'm sorry for your loss.
I just lost my dear very Catholic Mom three days ago, after a long time in hospice care. Like yours, my mother worried at the end about where she'd go next. Like yours, I believe that my Mom was afraid she hadn't earned her way to Heaven. Like you, this made me enormously sad and enormously disgusted with the church, of which I haven't been a member for decades.
Before she died, I assured my Mom that she'd live on and still be present in our lives. I made her pinky swear that she'd come back to visit me, just to tell me I was right. I'm waiting!