Is Girl,Interrupted a realistic portrayal of a mental hospital?

It depends on the hospital. Although psychiatry has moved on, the NHS hospital I was at was a complete nightmare, people only saw a Dr once a week. The place was underfunded, overcrowded, no privacy, dirty and riddled with mice with rude and overworked staff, just completely demoralising and unhelpful, yet they got an acceptable grade on inspection and complaints were never listened to. Mental hospitals on films and TV tend to be portrayed as being cleaner, more homely and efficient than they really are.