Joan, could you post a picture of the whole bush? How big is that pot? Is the rose bush a standard variety or a dwarf or miniature? (they do better in pots than big ones do)
Roses are heavy feeders and develop large, deep root systems, so I'm suspecting that overwatering isn't the only problem there.
My brother lives on Vancouver Island and has been bragging about the wonderful summer weather you've had up there. After a nice warm, sunny August, that rose should have canes as thick as your fingers and should be looking very robust. I think your rose bush has run out of nutrients in that pot. Repotting now with a whole lot of new soil, and some rich amendments like some alfalfa pellets (know anyone with a horse?) will stimulate new growth which isn't necessarily a great thing this late in the season. New growth is more frost-tender than hardened growth.
Unless you're prepared to protect that pot from freezing and frosts through the winter, I'd wait until next spring and start again with potting soil plus compost plus, plus aged manure plus any other rich amendments you can get. Use a slow-release fertilizer so it will have a constant supply and not run out. As soon as you see new growth in spring - little red shoots on the canes - start fertilizing.
