When I read "step" mom I instantly thought of people that I know who shared with me that while growing up, they felt like their "step" mom or "step" dad either hated them or refused to make any effort at all to like them. In their cases, it was really about favoritism. They were not their "step" mom or "step" dad's natural born children so they would not accept them as they would their natural born children. Which I think is sad and pathetic!
While growing up, I had always felt like my grandparents hated me and for years I blamed myself over it and tried to love them and gain favor with them, but to no avail. After becoming an adult, I eventually came to understand this was about favoritism. They did not like my dad (he was six years older than my mother and they thought he was too wild for her) so it rolled down hill on me. It really irritated me when I was young to see my grandparents praising or bragging about one of my cousins (whose parents they really liked) but I was treated like I was no good and could not do anything right.
Demi had great advice. Keep showering her with love and continue to pray for her and also continue to pray for strength and peace from God for you. I will continue to pray for you and your step mom as well.
God bless you my young sister in Christ!