Hi;- I am so sorry to hear about your loss. To me gardening is a great joy, easing the grief and I also belive it is
the best way to remember special loved ones. I lack knowledge of plants that would thrive in your climate zone
so I will offer my sincere sympathy instead.

No problem. I use white and night bloomers and some deep purple for depth. This year I'm growing white cleome, dame's rocket, 4:00s, lychnis, datura, alyssum, candytuft, irises, moonflower vine, white hyachinth bean vine, several artemsias, and white impatiens balsam. I grow the purple daturas and purple perilla. So far it looks like nothing, but this year it should take off a bit.

I have a friend who lost a white dog names Paxy and she is growing a white garden in her honor. It's a lot of fun.

Bless your heart! My childhood dog was a Weimaraner named Misty. I still remember the date she died, May 7, 1978. Weimaraners are silvery gray (misty) and so are Dusty Millers (artemesia, I think). Dusty Miller is pretty at night, and as someone else already mentioned, any white flower will be beautiful. Treasure your memories of your Misty; they'll last forever. And may your garden offer you some comfort at this difficult time.

I use artemesia Powis Castle as a foil for bulbs and other taller plants here in Zone 7. The aretmesia forms a nice 6-7 inch tall, lacey grey ground cover that lets the bulbs grow through. And it's evergreen (grey-green actually) here in zone7. Currently in bloom are some very light, almost white daffodils poking their heads over the gray lace of the atemesia. Later there will be various lillies and the datura will eventually wake up too. I have to re-plant moonflowers every year, and I usually put them near the back where they can mix-it-up with a honeysuckle I have growing on my back wall. I use a mix of lillies so there's almost always some in bloom from spring to fall. They're also good flowers to use for dedication gardens as they symbolize purity and innocence, and the restored innocence of the soul at death.

Best wishes

So sorry about your pet aka Best Friend. We lost Tiffy several years ago and still tear up at times, missing her. I did her garden with Moon Vine, Hosta, Ferns, lillies and Dusty Miller. We wanted it simple and very easy on upkeep. I also put a Solar light shaped like a butterfly near her grave so that we could see the little angels we put for her headstone.
Hopes this helps.