Look at your papers closely. You have
joint custody so that is very good. Anything that says about moving? Also, how old is child and do you live in same school district as child now so she would not have to change schools? Would child want to live with you full time?
Go to the family court near you early any morning and ask to file a petition for emergency restraining order so that daughter stays in same county/state until a court hearing as mother is stating she intends to move child within the next few weeks out of state without your permission. Put in there that it is in the best interest of child to have both parents in her life and father intends to stay involved as he has been the last XX years.
At same time, file custody modification petition that states "father requests residential custody as mother intends to move out of state within the next few weeks. Father has been involved in child's life and wants to remain in her daily life."
Send ex a text or email (and save it), follow up with a registered mail letter stating same thing to her address so you can prove she got it stating:
Ex,
I am not in agreement to have xx move with you out of state. I have been in her life and want to remain in her daily life here in XX. We have joint custody and if you insist on moving, I will file a petition in court that will allow you to move but for xx to stay and live with me.
You
Either way, you need to file in family court so that was a new
parenting plan is made. Since she is moving, the courts usually make her pay for all travel costs for visits (plane, gas for car, meet half way). IF child is school age, look a school calendars and come up with as much time as you can for you to see her or if you win for her to see child. Be ready for both ways so you can present a parenting plan either way. Did she offer you a parenting plan if she were to move to WA?
Filing is free or small fee and you can do it yourself at the family court. Ask where you file petitions (paperwork) and they will usually have blank copies to fill out and hand back in. In NY they type them for free for you. Call and ask what time they open and get there early. Also , call legal aid and see if you qualify. They may be able to at least help you with paperwork if needed. Legal Aid usually has office near the courts or in same building.