Any Parents out there? Please Help!!?

I have a 10 year old daughter who i get to see every other weekend. My ex lives in San Francisco. I live in Los Angeles. Every other weekend we meet in Fresno so i can have that weekend with my daughter. This weekend however my mother is bringing down my daughter to LA because my daughters cousin is having a birthday party. My daughter very rarely comes to LA or gets to see her aunt, uncle, and cousins. My daughter got into trouble with her mom. Not listening, going to friends house without permission. Twice. After the first time my ex told her if she did it again she couldn't go to LA to the birthday party. Well she did it again. So my ex grounded my daughter. She told me she wasn't coming to LA. Plans were made a month in advance for my daughter to come here. It is my weekend. I told my ex wife that it wasn't fair to ground her from coming to LA. She wants me to drop everything and meet in Fresno. Is this right? The ex is upset with me because i am not backing her on this punishment