Why is my 4 yr old grand daughter mean to her mom when I’m around?

[Gogocj]

I helped raise my grand daughter from the age of birth to 2 yrs old. We share a special bond. My daughter married and moved out and I’ve backed off to let them figure their new normal out. However, every time they come to visit or we go anywhere, she acts out to her mom and is mean to her. She tells me that she wants to live with me and will “play” call me mom. Her mom will swoop the kids up crying or upset and leave at that point. There’s been times where she will freak out when I leave her, begging me to stay. I’d also like to include that she has a 16 month old brother. They play well together but she can be the typical 4 yr old sister. Is this normal behavior or should I be concerned?