I have had 3 examples of past family contacting me after death.
My grandfather from father's side in a dream came as a voice, his voice. He told me to not be so negative. I felt then that yes he cared about me, he really didn't show it too much when growing up. He favored my cousin.
He came more recently again as a voice to let me know a living member of my father's family had just died.
His brother, my great uncle came to me when I was sixteen to talk to me about his health and his passing, and to tell my grandfather what he was telling me- to attempt to confirm, and shake my grandfather into realizing he was there, is here, and to let him know there is life after death. He also wanted me to pass the message along to my grandfather to let go of any guilt, and to start laughing more. My grandfather did start to open up and laugh more a bit- more-so closer towards the end of his physical life.
Another family member my grandfather on my mother's side, came to my mother in a dream to tell her something important in relation to me her daughter, but she would not listen to what he said, as her father and her had a lot of coldness between them, when he was alive. We never exactly found out what he had wanted to say.
So yes I have. It has seemed random, but isn't as there is a purpose, and they have made contact when they are trying to say something very important.
I feel this is the case with many people.
Cherish the memory of your step mother. :) I think very much your mother gave you the necklace for a reason. I do believe your step mom wanted you to have it.