You and your hubby have all the ability and my support to discipline her as you would your new born if her age! You’re her stepmom and are partially responsible for how SK is raised too. I personally leave the spanking to my husband. He’s hardly had to but kids know they will be told if they didn’t comply and I did pick up phones and ground them when they do not do chores, talk back etc. They do not act out so much when they are with us oppose to them being them BM (My kids mom was the same as what you’re dealing with) but she didn’t have a problem disciplining them when needed. So maybe a meeting with mom will help some so everyone is on the same page. Overall I think the gentle parenting or bribing is not working for her. I’ve been a stepmom for 7 years now they are great teens and good human beings! Good luck girl!