82 yr old o2 saturation level was more than 95% on ventilater but after removeing ventilater her o2 saturation drop up to 30% will she recover?

Depends: The cause of desaturation is the main way to tell the prognosis. She is on a ventilator so she is sick. But what is the cause? It also depends on the length of time she has been ill, the degree of settings of the ventilator. It is difficult to make a prediction without these informations.

Unlikely: Drop in saturation suggests she needs to remain on ventilator. Her advanced age and the disease that landed her on a ventilator will determine mortality.