I'm sorry for your loss, my friend! But it's as you write, sometimes, passing away can be relief and your mother for sure is in a better place now.
I lost my mother a long time ago and I once had a feeling like you. It was when I held my eldest daughter, a little baby then, late at night. I was was alone with her, trying to make her sleep and I suddenly felt the strong presence of my mother in the room. I even talked to her, presenting her grandchild.
What is very striking in this is that my eldest daughter comes closest to my mother in behavior and physical appearance. I think there are a lot of secret wonders in this world, we do not know anything about.
Have a great weekend, you and your loved ones!