You may also be able to buy grandma a prepaid card with her name on it that functions online as a regular credit card. I bought one once for someone and am now on AMEX's email list. They claim there are no purchase fees through 6/30/2015 if you use the code MDAYBC before 6/30/2015. In my experience, these work easily online.
https://www.americanexpress.com/gift-cards