My friend was in an accident following Nitrous Oxide at the dentist, is the dentist liable?

My friend is in the hospital following an MVA. I spoke with her and she had just been to the dentist and had Nitrous Oxide. When she left she still felt alittle strange, but had to be somewhere at 5:00. She exited the dentist and did not see the car coming around the corner and was broadsided. It was clearly her fault. But, is the dentist liable in any way for allowing a patient, under the influence get into a car with no one with her? Or was it my friend's responsibility not to enter her car until she felt "normal". The hospital did an alcohol and drug test and nothing was detected. I want to help her, as her car is totaled and she has 6 broken ribs.