In WA does a guardian ad litem have the right to request a juvenile's medical records, GAL

One answer could be that you always have a right to request but that doesn't mean the institution has a duty to provide it to you. Another answer is that this depends: did any court order the records while a juvenile sealed? are there any other restrictions on file access? do the records still exist in a recoverable format?

Basically if your ward can compel the records and you can show a reasonable request on why this is in the ward's interest to produce the records you should be able to have access. If not then look at their reason to refuse to decide your next course of action.