Trying to locate the lady that sat beside me on a flight from Vancouver to Toronto on Apr.12/10 to thank her for her help

Your best bet is to contact Air Canada Customer Service.

Explain the situation, and that you would like to thank this fellow passenger. Provide the flight number, seat numbers, date and time.

I doubt they would provide a name and address for you, but if you prepare a thank you, and as them to forward it to her, I can't see why they wouldn't help you do that.

Good luck.