A person can only do work suited to their abilities and training or education, so in this case, mentally challenged would not work.
Bi-polar often couples with genius, so it could work if it was only a mild version and she had back-up during absences while manic or depressed.
The principle (of equality of opportunity, pay and conditions in work) it means that the candidate with the best capacity to do the work gets the job irrespective of irrelevant characteristic.s such as gender, "race," hight etc.