That sounds a bit sketch. I would say no. I don't see anywhere that you can add a second.
I doubt you have two Food City cards in your name, so I am pretty sure ibotta would be the same
Several people have indicated their account was locked, and of course none of them said they did anything wrong......lol. So it usually is best to avoid doing anything that could appear suspicious so you don't have to go thru that aggravation..
I could be wrong. Maybe it is possible to do what you say, but it would be much easier to hook granny up with ibotta.
Keep it clean. If she has a phone, do all her transactions thru her phone.