Your link literally explains how to sue a doctor for malpractice after signing a liability waiver.
No waiver can claim that patients cannot sue their doctors for gross incompetence.
In most cases, this will involve collecting medical files, seeing copies of the waiver(s) signed by the patient, and proving medical malpractice or negligence by showing that:
The doctor in question deviated from an acceptable standard of care
The injuries came from that deviation
The damages came from those injuries
Which is straightforward in this case. The standard of care is not to give valproate to women of childbearing age except as a last resort, and valproate is known to have a very high risk of birth defects.