Mental health providers are nearly impossible to find in the Seattle area, no matter the insurance, or even paying cash.

For whatever bloody reason they just don't exist in anything near enough quantity.

Have you tried to find a new GP for an adult with private insurance recently? Many areas have a shortage in general. This has little to do with insurance coverage, and everything to do with the bad incentives of the medical profession. Who would become a GP with your MD, when you can make twice as much money as a specialist instead? It's like getting a CS degree from Stanford and deciding to become a sysadmin at a high school with it, instead of becoming a SWE.

Conversely, I'm surprised you found a dentist and a mental health provider that takes any insurance at all, and didn't have a months-long wait list. I've almost always had to self pay for both...

Yes, in fact several of the doctors I called would have been happy to take her on if she had private insurance. This has everything to do with insurance.