What does GAL stand for? (Perhaps I should know, but I have not run across this acronym before . . . Maybe it is something unique to Washington that we don't have in Texas.)
I would strongly suggest contacting the Guardian Ad Litem and the Court as soon as possible to let them both know of your financial situation. In cases like these, the best thing to do is to ask permission (i.e.: payment plan or something) rather than forgiveness (after missing a Court-ordered payment deadline). The GAL would probably be willing to work with you and if you have the GAL on board with a financial arrangement, the Court would be far more willing to change the Order.