I do professional psychic reading for people and it is not uncommon at all for those who have crossed over into spirit form to make their presence known and leave messages of comfort/love/support/presence for the person I'm reading for. In some instances long two way conversations in which I just act as the conduit/translator, while the two communicate back and forth on complex issues.
I've even had people be brought to me by Spirits so they could move messages and comfort to the person. I'm getting to understand now that when a person shows up in front of me with a perplexed look or slightly spooked look on their face and say "Why am I here?" or "I feel utterly compelled to come to you but don't know why." that it is likely someone who loves them and is no longer in body that wants to communicate to them.
I conceder myself a poor channel at best, there are so many who are much better at this than me, but sometimes I'm all that's available apparently.
I think it's a beautiful act of love that your step-mother is still in contact with you and letting you know you aren't alone and that you are well-loved. Magical indeed! You are very blessed :)
"If you want to understand the Secrets of the Universe think in terms of Energy, Frequency and Vibration"
Nicola Tesla 1856-1943
When asked by a reporter how it felt to be the smartest man alive Einstein responded "I wouldn't know, ask Tesla."