In the HR world, two words strike fear into the hearts of employers: reasonable accommodation. The phrase (and its surrounding rumors and misunderstandings of the law) conjures up images of expensive changes and potential lawsuits. One tool which should - and often must - be considered as an accommodation for employers under the Americans With Disabilities Act (ADA) is unpaid leave.
An open-ended period of unpaid leave is not required to be granted under the ADA. Therefore, if neither your employee or a doctor can provide a date upon which the employee can return to work and perform the essential tasks of the position, then granting such an indefinite period of unpaid leave will not be required. Most periods of temporary leave would be considered reasonable accommodations if the employee requests them.
The best approach is to communicate with your employee about how best to address her needs based upon the recommendations of the doctor. This is especially true in cases of mental health issues such as PTSD, anxiety and depression, in which short periods of unpaid leave can significantly improve the health of your employee and allow her to continue to work. In fact, many legal cases in which employers were held liable for ADA violations involved their refusal to grant unpaid leave. As always, consult your attorney for assistance, and educate yourself about ADA requirements to prevent unintended violations.