What type of complaint or document do I need?

If you want to prevent Mom from taking your daughter to live in Seattle either temporarily or permanently, check your order for a restriction that states the mother may not move your daughter out of the State. That provision will be enforced if you take the Mother to court to enforce it with a Petition to Enforce the geographic restriction.   You could also file a Petition to Modify the court orders and request primary custody of your daughter.   If there is no restriction in the court order and you do not want to request custody, then your recourse will be to wait until after the mother has failed to turn over daughter at the time and place the order states you are supposed to be able to get your daughter at the beginning of your possession periods.  This is a highly technical type of suit for which most people need an attorney's help. My concern is that this is a time when both Mother and daughter need you to be flexible and understanding.  You are not, of course, required to do that.  If you do not think it is in your daughter's best interest to be the caregiver for her mother in this situation, or for your daughter to be taken out of her school, then you may have grounds for a custody change.  Maybe you would want to compromise and offer to take care of your daughter here but to pay for her to fly up to see her mom a couple times.  On the other hand, maybe you could consider visting your daughter in Seattle while she is there with her mother.  While you may miss some of your visits, you will still have an opportunity to spend time with your daughter, and both she and her mother will likely appreciate the efforts and expense you go to in order to accomodate mom's serious illness.