I LOVE that pic!!!! What a precious little girl!!!! I think it's simply lovely that you are doing this with her and for her and those clematis are the most lovely I've ever seen...especially that blue one!
You just gotta show the progress pics along the way so we can see it take shape and bloom. Makes me want to be a little girl again!
There are a lot of native flowering bulbs that could add color, and be suited to the rainfall in your area. Blazing star (liatris) was one my paternal grandmother loved. Camassia has the virtue of being attractive and also being edible, - theoretically. If I had my book on North American bulbs to hand I could offer other thoughts.
I'll be planting a clematis along the arch over my garden gate this year as well. I'd also like to plant a honeysuckle there....I LOVE the smell of honeysuckle. Both are vines that need very little care and thrive well in the acid soils here at my place.
I've also found another vine we really like and that is very cold hardy lately, though they don't vine as quickly or as high...found it at the local nursery last year but for the life of me I can't remember the name of it. Deeply red, velvety textured trumpet like flowers, waxy leaves, bloomed like crazy and put out runner vines that climbed but not many of those so the plant stays more shrub like. They also had this vine in pink but the red was so deep and entrancing that we liked it best.
I'd like to plant some of those inside my garden fence so they can slowly vine upward and bloom those scarlet blossoms from early spring until past first frost.