The victim, identified as Morgan F. Williams, 58, of Seattle, was a 32-year employee of Eddie Bauer, and her ex-husband says she was on her way to work when the crash happened.
The eastbound lanes of State Route 520 were closed for hours following the horrific crash, but have since reopened.
Washington State Patrol officials said a 1996 Ford Explorer going the wrong direction in the eastbound lanes of the freeway slammed head-on at high speed into a 2003 Mazda Protege being driven by Williams near the Montlake exit at about 5:25 a.m.
Firefighters had to cut the roof off of the Mazda to rescue Williams, who was trapped in the mangled wreck. She was taken to Harborview Medical Center in critical condition, and died of her injuries at about 10:45 a.m.
The driver of the Explorer, identified as Michael Anthony Robertson, 25, of Tacoma, was under arrest at Harborview, where he is being treated for a leg injury. Charges are pending against him.
Washington State Patrol Sgt. John Sager said investigators believe Robertson may have been drunk and apparently made a U-turn on the freeway.
Court records show that Robertson was previously charged with DUI stemming from earlier incident in December and was scheduled to stand trial later this month.
The victim, who grew up in Oak Harbor on Whidbey Island, was well-known to family and friends as someone who was always there to provide support when needed.
"Morgan Williams was the constant. She was always there," says Mark Funk, a friend who had known her since they were children together in elementary school.
"She loved her kids. I talked with her daughter this morning. She cried. She said, 'I was at mom's house last night, and I got her last kiss.'"