Thank you for writing. In psychology, the term “projection” is when someone projects (like a film projector) their own feelings onto another person. Your stepdaughter says that you are jealous. It looks to me like she may be projecting her jealousy on you.
You are only 10 years older than she is so it’s not possible for her to think of you as an additional mother in her life. To her, you are a competitor for her daddy’s affection, attention, and even money. I’m guessing that she has strong feelings about the divorce and, consciously or unconsciously, wants to undermine your marriage. Apparently, she and her mother agree about this, which complicates things even more. The daughter is acting as her mother’s spy in a divorce that doesn’t look like it’s over — at least for her mother.
Your husband is caught between his love for you and his desire to be loved by the daughter he loves. It is understandable that he doesn’t know how to navigate this very difficult situation.
I strongly urge you and your husband to see a licensed family counselor about how best to deal with his daughter’s feelings and behavior. You two need to be a team. A counselor will help your husband figure out how to love and support both you and his daughter without endangering your marriage. You will be helped to understand how to support him and how to navigate your own relationship with the daughter and her role in your children’s lives.
I wish you well.