Hi Lukedra!!
I think that this woman left the cards for you.
Is ok you using that, in fact they was for you at the first place.
Maybe is a gift your step mother gave you a gift accept it.
Don you think weird she onlystarted at tarot when she was dieing?
Coincidences doent happen. I found my first deck at a bus station, so a person bought it thinking on using it, but she didnt, I did.
So someone wanted me to read tarot and it was the way she made it.
Your step mother next to the death turned more clouse to spiritual life, so she bought a deck. She died but now you have it, is her heritrance.
If you feel bad shufling it so buy another one, but if you dont it´s yours.
I belive at this, she bought it for you, even if she did that whith out waiting that.
For my experience, i think you will be a great reader.
By the way, what deck she left for you?