Depends on what you like, as you are probably aware, you can never count on good weather in Washington and Oregon, plan on rain, then if it is sunny, that is a bonus!
The Oregon coast line is generally a lot more scenic and easier to enjoy by automobile than Washington. You can drive on the beach at low tide in Washington at Long Beach, but you had better know what you are doing, seen quite a few people get stuck, and vehicles ruined when the tide came in, entertaining to watch.
You could spend a night at the Great Wolf Lodge in Grand Mound, Washington, which is a water park with lodging, depending on if your daughter enjoys that type of thing, then you can either continue south on Interstate 5 to Portland, or take Hwy 6 over toward the Washington coast, cross over the Columbia River, then Astoria and Cannon Beach in Oregon are places to check out, then you can head east to Portland.
Mt Hood or the Columbia River gorge are well worth exploring, lots of trails and waterfalls in the gorge.
Skamania Lodge on the Washington side of the Gorge is nice, a little pricey for my budget, but might work for you.
Be prepared for all sorts of "characters" in Portland itself, it is an interesting city, personally I am glad I don't live there, but a lot of people love it.