I think your best option is to buy an Apple TV ($99, USD). Then, while on FaceTime, your grandmother can send the image to her TV (that you've hooked the Apple TV up to). So, she holds the iPad2 in her lap so people can see her face and then looks at the TV to see the person/people she's talking to. All wirelessly (as long as you have wireless in the house).
If may take a bit of fiddling to get everything 'just so," but this is the best I can think of...
Marilyn