How do I get rid of this dog as humanely as possible?

OK, I admit, this is very evil of me to think this and I am probably a Troll. I won't probably do it, but i'm asking anyway. Before you begin, It would be ok to call me your choiciest names possible because I probably am them. Anyway, I have this 16 year old dog and she is probably gonna die in a year. She is Barking MAD.(literally, BARKING mad. ok, bad pun.) She won't shut up! when she's not barking she just sits there in sleep. She also has a lot of things wrong with her like joint pain everywhere. I want to get a new dog, But I can't until she dies. It,s really my grandmas dog but of course, she thinks it's a perfect angel. So we can't give it to a pound, which I would like to do. Any thing like, painless death pills or something that I can get at the store? Or should I just feed her a bunch of grapes, because that's what gramma gives her a lot.