My rule of thumb is generally that if I can afford the treatment without missing out on something important, like putting food on the table or making my mortgage payment, and if the treatment is likely to restore them to reasonably good health and quality of life, I will attempt to treat them. There are certainly piggies out there who have lost an eye surgically or gone blind via a natural process like cataracts who have recovered very well and led good, happy lives, so I wouldn't assume that her quality of life would diminish with the loss of an eye. Only you know your financial and can weigh whether or not this treatment is in your ability to provide for her. Some vets will offer payment plans and things like that for medical treatments if the lump sum up front is hard to make. Lots of luck, it's never easy to decide what's best for medical treatment!