I'm really sorry this is happening to you. It sucks that we have little to no protection under US employment laws.
Employment laws in the US generally favor the employer. Even though you've given your boss advanced notice and medical excuses for absences, she obviously feels she can't rely on you. Employers, especially in small businesses, count on their employees to be at work.
I'm guessing this is a small business. Too bad, because FMLA is only available to employees who work for companies with 50 or more employees.
Regarding reasonable accommodation, flexibility is built into the reasonable accommodation obligation under the ADA for the employer. For example:
1. employers can choose among effective accommodation options and do not always have to provide the requested accommodation,
2. employers do not have to provide accommodations that pose an undue hardship,
3. employers do not have to provide as reasonable accommodations personal use items needed in accomplishing daily activities both on and off the job,
4. employers do not have to make an accommodation for an individual who is not otherwise qualified for a position, and
5. employers do not have to remove essential functions, create new jobs, or lower production standards as an accommodation.
Reality is that some jobs require an employee's physical presence at specific hours. Alternate hours and working from home are often not an option and there is no 'reasonable accommodation' for that.
Check to see if NC is an employment-at-will state, which gives the employer the right to fire an employer for any legal reason.
Unfortunately, it is up to the employee to prove that the firing was illegal - it is rare that they are illegal. Cruel, immoral, unethical perhaps, but not illegal. Unless you can get an attorney to take your case on contingency, it is very expensive to retain one to fight these types of cases.
Good luck!