Should I be mad?

My daughters father is in jail for a year. My daughter and my son went over to his moms for the weekend since I work a bar job and she let his new gf who hes been seeing for only a month or 2 pick my children up from her house and take them to the jail to see him. I have previously asked her not to allow this woman around my children because 1. Shes already asked my daughter to call her mom and 2. She slanders me to my children every chance she gets. Am I petty for taking the children out of grandmas life because she won't respect my wishes and told the kids to lie to me about it.

If it were me, I would tell her one last time that she is NOT allowed to take your children, & if she lets her there will be consequences. If it happens again, then I would not take them over anymore. There’s no reason for this lady you don’t even know to be taking your kids places, and no reason for his mother to not listen to a simply task.