Could it be healthy for a 16 year old girl to masturbate about 3-4 days in a week?

This is normal: Many, perhaps most young women enjoy their bodies in this way and this often.

Sex and Doctors: Of course. This is normal, common and of no concern for your health. Sexual activity is usually a sign of health. Masturbation specifically is a common and natural part of the human experience and there are no negative health consequences to this activity.