My wife was fired from her job this week and we are wondering if we have an ADA complaint.?

She informed her work 3 months ago that a Dr had said she had a memory problem and was on Alzhimers Meds. There was no official diagnosis. Her memory was not improving and she was making mistakes at work. Her employer kept a record of her mistakes, offering no assistance or offering to move her to another job. She was fired on monday, after 15 years of service, for the volume of mistakes she made over the last few months. We are wondering if they violated the ADA laws?