Is it always necessary to get POA for one's parent?

I am my mothers caregiver.I don't live with her but just around the corner in the same apartment complex. She is able to live alone in her apartment but I do some of the cleaning and all of the shopping. She can't and does not drive. She gets around with a lot of effort with a walker. She still pays her bills and pretty much manages her money (I do give her input in this area as we do discuss things since I do her shopping). I have 3 other sisters. We all get along and communicate freely with each other in regard to my mom's well being. We all have a good relationship with mom as well. I have noticed that her memory is not as sharp, she is thinking more slowly, and the past is more vivid than recent activity at times. She does have an Advanced Directive. She does not own any property or have any assets. Taking all this into consideration I am wondering if a POA would be necessary. She will be 89 in a months time. Thank you.