Was there a reason why she was never a part of your life? Is there a possibility that you might now want her to be part of your life? If you don't, will you one day (when she passes away) regret not taking this current opportunity to 'make up' for the past? Depending on your answers above, proceed accordingly.
If you don't want to renew the relationship, you will just have to find a way to let her know it. Except, she might forget what you told her, and she will call you again asking the same question.
If you want to renew the relationship but on a limited basis, then tell her so. You set your boundaries and keep it. Of course, she may keep forgetting and try to push for more in the relationship. Don't let guilt enter. Look into your heart and go with what you want and will not regret later on.
How old is she? Do you have siblings? Would it be so terrible to meet for lunch? How far does she live? If she can use the phone, she is still mentally competent.
If you don't want to renew the relationship, you will just have to find a way to let her know it. Except, she might forget what you told her, and she will call you again asking the same question.
If you want to renew the relationship but on a limited basis, then tell her so. You set your boundaries and keep it. Of course, she may keep forgetting and try to push for more in the relationship. Don't let guilt enter. Look into your heart and go with what you want and will not regret later on.