A.M.
Ok I'm brainstorming!!
How about Tahoe? Or Aspen? A white pet brings to mind snowy ski resorts.
You can google "ski resorts" and maybe one will have a name or is in a city that you just love the sound of.
Even Vail,Vienna,Everest,or Whistler sound nice.
Also that comes to mind are movies that have a lot of snow or white,such as the Neverending Story or Chronicles of Narnia. Narnia is a pretty pet name. I believe the name of the land in neverending story was Fantasia. And the flying white dog's name was Falcor but that doesn't sound too cute for a girl pet.
Other white pet girl names I like are Moon,Shasta,Britanny,Bunny,Celeste,Phoebe,Penelope,Polly,Crystal,Star,Bridget, Shooga(for Sugar),Glitzen or Glitz,Jazzy,Jackie Frost(call her Frost),Icie,Glacier,Coco(for coconut or even Coco(nut) Chanel),Pearl,Diva,Zsa Zsa,Pina (for pina colada)..
or you could go the white sand beaches route;
Figi,Maui,Lulu(honolulu),Tanya Bahama(like tommy bahama),Tahiti,etc
or think ice skating.
or cold destinations like Russia or Antartica. You could name her Arctica.
here are other name ideas:
Blizzard,Cloud,Daisy,Ivory,Opal,Shimmer,Spirit,and duh..Winter.
:)