Fibroids after menopause is a joke, that can never happen. As a medical student in Gynecology department, we always made that mistake, it was drilled on us like nails on wood that it can never happen. So you have to check on other things, at her age it could be anything from her breasts, ovaries, stomach...have u had an ultrasound done? breasts checked?
Go back to another doctor and have it fully checked now, i mean bloods, chest xray, abdominal ultrasound and x-ray, urine test etc. Too bad we cant help the other doctor, (s)he is too far lost.