Creating a will lets your mother name an executor, who will file her last tax returns, notify social security and the state department of health after her death, cancel her cable subscription, and deal with her overdue fines at the library. It's just good house keeping and will (no pun intended) make it easier for you to tidy up her affairs after she's gone. More than that, you may not know everything about your mom--some of those odds and ends may surprise you.
Having a will in place will make it possible for you to deal with whatever she leaves behind. My very own Dad, for example, left my sister and I an oil and gas lease in Oklahoma (we call it 'the gusher') that we had NO IDEA he owned. Wills aren't complicated, she can do one herself using Nolo's online Will or Nolo's Quick and Legal Will book. And here's something else she needs: a Durable Power of Attorney and an Advanced Health Care Directive. These documents will help you to take care of her when she gets sick. The Power of Attorney allows you to take care of her financial matters: the Advance Health Care Directive gives you the authority to make medical decisions for her if she can't communicate directly with her doctors. You can make both of these using Nolo's WillMaker, and local senior centers can often help you get free forms to fill out as well.