Help! What do i say???....?

Well, my step mom used to yell & blow up ALL the time & i never was comfortable just confronting her about things afraid of her reaction. Now shes calmed down & wants to bond the way i do with my mom, but everything she suggests just doesn't work. Ex// I'm going to New York for a school trip & she wanted to chaperone - def not going to happen. I waneted to take sewing lessons for fashion design, & since she sews wantd to help me but i also told my mom abut it, & she got mad because i told my mom, and im like - i just told her because my stepmom didnt actually do anything with me yet. So basically i want to explain to her about the whole sewing thing but its hard as she never wants me to mention my mom or she gets angry, so how to i tell her without getting a bad reaction & getting my message through??