Hello! I highly recommend spaying your cat, that is great that your mom is planning to do it. She will be much happier, less annoying and a lot less likely to get cancer and diseases when she is older. Anyways, I would go here: http://www.abbeycats.org/about.htm
And contact them through email or by phone and ask about low cost spay clinics in your area. I thnk they would probably be able to help you find one.
Good luck and great job on getting your cat spayed! She will thank you!
You can also call call 1-800-248-SPAY and see if they have recommendations for Canada too. I don't have specified if they are US only. But it woulodn't hurt to call and see.