I had the same problem where my foster daughter is buried. To be clear, she was with us for 12 years and was only legally not ours. Anyway someone would take the stones from her stone which is our tradition and flowers as well. I really lost it and suddenly was filled with calm as I realized that she is not there. That is where her shell is buried in an unnatural way. She is here in this home, in the memory tree we planted, in the pictures of her living. Yes, it is tradition to go to the grave but for me I found that once I released the grave I had more peace. Good luck. (by the way your step mom seems depraved)