Grandma is actually a single entity, a witchlike creature from another dimension that subsumes older women into her dark service. Her actual name is Grrrr'And'Mandala, goddess of wheelchairs. Her loyal alzheimers-inflicted subjects will try their best to make your life hell and, eventually, kill you, claiming it to be a "lapse in memory" should you survive.
Unless you kill your tormentor first. Don't try to sneak up on them or beat them up. With grandma, a direct approach is quite possibly the most foolish thing that can be done. If you can set it up right, the best way to get rid of old bag o' bones is to lure them into a spikey acid-filled pitfall. try to get some classical music into the mix as well, as this will sever the link to her dark queen, and the empty shell will begin to flail spasmodically. This is usually mistaken for the effects of some old-age disease or, less often, dancing. It will give you an edge over the horrible Grrrr'And'Mandala and her minion.
Of course, not all grandmas will be foolish enough to leave their two greatest weaknesses just lying around (though the pitfall is remarkably easy to put together). If you do not know where to find prunes or bad music, see if you can employ the help of a grandpa. They won't tell you, but grandpas are a sort of mortal police for Grrrr'And'Pandala, the God of overused "Back in my day" statements and brother to Grrrr'And'Mandala. They always keep the materials needed to dispatch an unholy minion close at hand, and can use a good deal of illusions to confuse the evil creature (how else could grandpas and grandmas remain married to each other for so long?).
Unfortunately, ol' gramps is still only mortal, and the risk of him passing away prior to the extermination of the beast in your house is not ignored by us. Should he be resting six feet under right now, root around in his "empty" room for something. Failing that, beat a hasty retreat to the nearest clothing store. Grandma's still a woman, after all, and will be distracted by all the new fashions that are already on sale. This will give you at least an hour or so to prepare a mor elaborate plan, or at least root around in gram's closet.
Don't assume that the pitfall mentioned earlier is the only way to get rid of your "beloved" grandmother. Other solutions include the foolproof stake-to-the-heart. In fact, it really is foolproof, because if the steak (should you mess up) is fatty enough, it will probably send grams into cardiac arrest, or at least give her diarrhea. In fact, really any weapon presumed to kill mythical beasts is a good choice, from the stake, to silver, to three-hundred severed monkey phalluses (some myths are weird, okay?) dropped from a bucket onto the head region. Grandma may be an instrument of destruction, but she's no piranha. She has weaknesses, if you know how to exploit them.