WA Guardianship question... Can the Guardian of a disabled ...?

That is a question for the court to decide. If the father pays support for the care of his daughter and visits her regularly, he might have a case for restricting how far away the mother can move the daughter. If it impedes the father from seeing her and checking on her, then he should take the case to court. If the matter wasn't mentioned in a prior court order and there isn't any contention, plus the mother needs to work to support the daughter---then she probagly would have the upper hand. At any rate, it should decided in court so there is no question.

Every guardianship decree can be individualized. In general you can't take a CHILD out of the state without permission of the noncustodial parent or a judge. I would assume the same would be true of a developmentally disabled adult, but I don't know. I have guardianship of my niece and her parents don't have any custody and they don't get any notification.

that depends on the court order for the visitation rights & if iron-clad, it might be as as simple as getting dad to agree