If your case would rest on the possible misdiagnosis and accordant treatment, not only should you see a lawyer, but another psychiatrist to confirm that it's a misdiagnosis, if that hasn't already been done.

I think leejosepho has pointed out the basic questions that would arise - and presumably your mother consented to this treatment and signed forms to that effect - which ought to include statements like she'd been warned of side-effects, etc. I was on lithium briefly and told to stop or contact her at the first sign of x y z, did he not do that?