Most of the massagers will list on the box " use with caution with pacemaker".
I won't get any interference with using a massager. I get interfere from the Toll charge from Singapore and Malaysia when I sat at the front seat. When it beeps, my heart rhythms became irregulars, messy and funny.
Check it out with her doctor or technician as Momto3 said.
Your grandma will be glad to have a grandchild like you.
That's a great question! Your grandmother is lucky to have you : )
I'm not a doctor, but off the top of my head I can't think of a reason why the foot massager would interfere with the pacemaker. However, I would definitely call (or email) the doctor to be sure.
You might also want to send an email to the PM manufacturer to get their direct input.