My story is probably like most of yours when it comes to blended families.
My daughter Bee is 13 and her father and I divorced when she was 5 months old. I remarried when she was 1 and a half yrs. Old. Her father got custody when we first divorced, but I got custody back when she was 3 years old. Her father and grandmother have visition with her one weekend a month each. They do not take her to church at all, the grandmother tells her if she moves in with her she will not have to go to school. The list goes on and on of what my daughter has told her counselor of what her grandmother has told her. My husband now and I have a 5 yr. old son Matt and 9 yr. old daughter Jessica.
Bee constantly goes around telling Matt and Jessica that they are her step-family, even though they know that already. It upsets Jessica because her grandmother, my husband nows mother treats Bee as if she is her legal granddaughter. Bee says she does not like any of us. We take her to church every Wednesday and Sunday when she is home, not at her dads or grandmothers. We have the same rules for her as we do our children, but she keeps telling Jessica and Matt that she hates them and does not want to live here anymore. Bee biological grandmother told me on the phone that Bee had told her she was either going to commit suicide or runaway from home and go live with grandmother or dad.
Bee has not said this to anyone else; not her counselors or anyone else in the family, so I do not know whether the biological grandmother is making it up just to get me to worry or if it is true. I have informed her counselors about it and they are going to see Bee on Wednesday. My husband and I are trying to not take it serious seeing as whom it is coming from since the biological grandmother has said one thing and done completely the opposite thing, stabed us in the back, so we most of the time do not believe her.
Any help is helpful. Thanks

Tell grandmother to tell the child the truth about having to go to school or you will go to court and stop her rights to visit the child.
And if she don't do it, if she is lying to the child, you may get the court to order that her visits with the child may be limited.

Let me see this is the same grandpartnet that is lying to the child about going to school. I would say if her mouth is moving she is lying from what you are saying.

I wouild also have a discussion with the father, and let her know if these lies continue you will have to take him back to court to limit his vistis as being a risk to the child.