What can be the cause of vertigo in a 30 year old woman pilot in steep dives?

Inner ear irritation: It is possible that the steep dive leads to negative pressure in your middle ear which in turn is causing irritation in your inner ear. The inner ear has a membrane called the round window which can be irritated by rapid pressure change leading to vertigo. You should see an ear specialist for a further evaluation.

Illusion: During rapid acceleration such as during a steep dive or if there a sudden change in airplane attitude, the balancing system of the inner ear sends a signal to the brain. This signal does not match the signal that the eyes are sending to the brain. Vertigo occurs.