Hard as it is, I think you have answered your own question.
Its all down to quality of life, and if she is confused she may be worrying herself, and that in itself is not fair. I have a fifteen year old who has gone deaf, and although she potters around and goes for walks with the others sometimes she seems to forget what she went into the kitchen for and comes back looking puzzled. Having said that, I do the same!
Get her checked by the vet, but please think long and hard whether you are keeping her going for her sake or for yours.
Better a day too soon than a minute too late.