She also has a 10 year old sister. Not sure if that makes a difference.
Sure she can ask but in order to change the PP you would have to either file an agreed modification of teh PP or a Petition to modfy. In Wa. , a child may never choose where he/she wants to live-- that decisioin is left to the sound discretion of the court and the parents -- kids don't get to call the shots.
Custody issues are never resolved only because of a child's wishes. However, you should interview a good family law attorney about the details to see if you have sufficient grounds to petition for a modification of the parenting plan. It’s always best to consult with a good family law attorney to discuss the details before you act. See my AVVO Legal Guides on modifications for more information about the legal issues raised by your inquiry. Click on my photo. On my AVVO home page click on "View Contributions" or scroll down further and click on "Legal Guides." Scroll down the list of my 29 Legal Guides and select the topics relevant to your question. If you like my answer and Legal Guides, please make sure you mark them as “helpful.”