My 74 Year Old Mom Has Been Having Vertigo And

My 74 year old mom has been having vertigo and severe headaches. She saw an ear, nose and throat doctor and they could find nothing wrong with her ears or that her ears were causing a balance problem. She's had three falls over the last several months without injury. Now she is experiencing weakness- having to rest after dressing and fell backwards- suddenly- the other day. The vertigo waxes and wanes in severity but she feels dizzy all of the time and nauseated as a result. She is refusing to go to the ER and has an appointment with her eye doctor in May and wants to wait until she has her eyes examined. I'm at my wits end! I am very concerned.