Dude. Guilt trip your grandmother bro.
Say things like "Grandma, does that feel right to you? that you take all the money I won?" Why didnt YOU enter the code grandma? at least half of that money should be mine! "granny, what are you going to do with that furniture after you croke?" ..
"give me the money or i'll break your hip"
Old people scare easily bro. See, even your sweet grandma will stick a thumb up an *** or two when 10gs are involved. even yours. she doenst give a ****!