A check of our NWMLS does not show the house being listed. A check of the King County Tax Records does indeed show a sale that closed on Sept 7, 07.
Contact a local title/escrow company and they can provide you all the info that is public record. You can find out which company or attorney executed the documents. Your aunt Dorothy would have been personally present with a notary to sign closing documents and they should have a forwarding address to transmit the proceeds of the sale.
For security and privacy sake, I will leave the rest of this search up to you. Some entities may want you to appear in person to verify. It is a sad comment, but in our day and age there are so many scams, folks are less helpful than they used to be. Hope you are able to find her and reconnect. Take care.