Plus, if she is unable to do her work due to sight limitations, it would be difficult to determine what a reasonable accommodation might be--especially if she is also unable to report to work due to medical treatments such as a series of eye surgeries.
You also are not legally bound by the Family and Medical Leave Act (50 or more employees). So, you do not have to provide a specific amount of unpaid time off work.
Your choices are:
1. Offer her a personal, unpaid leave of absence for a specific period of time (e.g., 30 days), clearly indicating in writing that she must submit medical documentation at explicit intervals to receive consideration for the continuation of the leave (e.g., every 30 days). You need to make it clear that there is no guarantee her job--or any job with the company--will be available for her if/when she is able to return to work.
In this instance, you would also want to specify that in order to return to work, you will need a fairly detailed statement from her primary physician that she can return to work and what her restrictions will be, if any.
With a personal leave of absence, the employee should also be informed that in order to keep her health insurance coverage (if same is offered through the company), she must pay the full cost of the premiums by the first of each month. Otherwise, she may receive 30 days notice of her health insurance coverage being canceled for non-payment of premiums.
2. Terminate her employment and simply say that if/when she is able to return to work, you will be happy to consider her for any job available for which she is qualified.
No promises, but not exactly a tightly closed door, either. Again, as you have less than 20 employees, you are not legally required to offer COBRA. But in some states mini-COBRA is offered, so she could continue her health coverage through that type of program if it's available.
3. Continue doing what you have been doing about this matter, which appears to be coping somehow with no one doing her work or others picking up the extra work as they can.
I think that the ethical question may not be as much about her job but whether she will lose access to health insurance coverage if she loses her job.
Without knowing more about what you can and/or are willing to do for her in these regards, the ethical question is best left to you, as only your own conscience and the fiscal realities of the enterprise can help you determine what you choose to do.