May we terminate a disabled employee who can’t perform an essential function?

Q. One of our employees was hired to a position that requires her to drive to customers’ offices. When we hired her, she reviewed and signed a job description that included a statement “that transportation was an essential function of her job.” Public transportation is not a realistic option. She recently received test results suggesting she might be suffering from multiple sclerosis. She provided a return-to-work slip indicating she would be able to return to work on a part-time basis but would not be able to drive or do heavy lifting. We told her we cannot accommodate her restrictions, but we provided a four-month leave of absence. Assuming she will not be able to drive when she returns, are we within our rights to discharge her? Are we going to violate her rights under the ADA or Michigan disability laws? ...