I wouldn't disclose PMDD to an employer unless she needs an accommodation for the condition (maybe time off?). As far as I know, no condition must be disclosed to an employer if the employee isn't asking for an accommodation (i.e. something to be changed on their behalf). There's no reason to set people on edge when there's no reason to believe the condition affects her work. I just don't think it's appropriate to disclose a diagnosis without reason, whether that diagnosis would be considered serious or not. My brother was diagnosed with schizophrenia 9 years ago and years later other doctors disputed that diagnosis. So I guess what I'm saying is -- things can change.