Am so sorry that your little one had to leave for the Rainbow Bridge where she is free to run now.
White Shakers Syndrome is rare but it does happen. Was your vet sure this was the case? Most Vets do not know about WSS at least this was the case with my little one years ago. I had to ask him if he thought it was White Shakers Syndrome. I went to see a Specialist and he knew with in 10 minutes. I would hope that today they do know more.
Here is a link for you as an FYI.... http://www.malteseonly.com/shakerdog.html
I haven't heard that this could affect their legs like your little one :O(
Can you tell us what symptoms was she showing that lead to him saying it was WSS?
Was she acting like someone with Parkinson's? Did her head shake when she was resting meaning with her head of the floor? Most times the shaking would stop if they were at rest/sleeping? The nervous system nearer the back of the head begins WSS....their white cells for some reason will begin to wear away/attack the covering on the nerves. Steroids would help and most times end the WSS. There are times with a little one would have to be on meds for a life time.
If you look at past posts on the forum you will see more discussions of WSS.
Yes, sometimes this can be genetic. You will have to watch your other little ones for any signs. If this should happen I would suggest going for a 2nd opinion at a different vet.
Please let us know how you are doing.