If you absolutely cannot find any rescue services near you, you might be able to place the dog in a US rescue. First, find and contact potential rescues in the US. You could check out a pet transportation service such as Operation Roger. I know they have transported animals from the US to Canada. Of course, this might not be what your mother would prefer to do.
Has your mother tried to find the dog a new home herself? If you have any pet stores around you, they likely have a board to post animals for adoption. Also, she can put an ad in the newspaper and there are plenty of online places as well. Try asking here in the rescue forum. You can also post here:
http://www.pets.ca/forum/index.php in the "rescue (adopt) a dog section. Post the dog's info and your mother's situation and see if anyone is willing to help. While rescues are nice, I'd assume it would be better to know the dog has found a new, loving family.