Vertigo problem. Can anyone help?

My mother is suffering from vertigo for the last 7 years. She has undergone treatment from various doctors including neurologists and ent specialists. She had even taken physiotherapy sittings. But there has been no improvement in her condition. She still gets high intensity episodes of vertigo on a regular basis. And most of the times she gets it when she turns left or right while sleeping or when she gets up or when she lie down. She has not had a sound sleep for the last 7 years. She constantly remains in the fear of having an episode everytime she goes on a bed. Neurologists say it's due to migraine. Ent specialists say it's BPPV. None of the treatment has really worked so far. She is still suffering. Can anyone help???