You wrote: "The tag SAYS the Daisy will go to -40 temps"

Nope. Not if it's Osteospermum. Perhaps +40 degrees?

I'm not sure about the privet, but Osteospermum is perhaps the plant most commonly called 'African Daisy' but I have heard that name applied to a few other plants. O. barberiae is hardy to at least 0F - I don't know of any Osteospermums hardier than that. The only other thing like that I can think of that might be hardy in Spokane is Gazania linearis 'Colorado Gold' which is from Africa and is hardy to about -20F. It should do well in Spokane with good drainage, but it is not cascading. For a cascading perennial, you might consider some of the low-growing Phlox species and varieties. I'm sure there are many other choices as well.

Aubretia, Arabis, and Alyssum saxatile are all perennials that will cascade down a wall but they bloom in early spring.