My aunt (86) forgets events, has poor eyesight and mobility problems. Should I get a Durable POA before she's unable to sign?

She trusts me. She has a son, diabetic and on dialysis. Because all the medicines he takes, he sleeps long periods of time. He does not do things for her at all (actually, he needs help) I have to assist him too sometimes! I stopped working to assist her full time. I am 64 and not too healthy, arthritis in both needs and elbow. I hurt my lower back and so on. I am the only one healthy enough to do house maintenance and manage the finances. If I get sick, we all are in trouble! Between her income and mine (SS and small pension) we manage our living expenses.