My friend has a strict Mom

My friend and I have had a friendship for 6 years. She is now a senior in high school, 17 years old; and is dating a guy in my class. I'm a junior. Her mom will not let her do anything to the point where my friend was tested for depression and she is clinically depressed. Her mom doesn't let her do anything bc her mom is worried ab her 14 year old daughter. She's too afraid to say anything to her Mom to get her Mom fired up. Yet my best friend is a very independent strong lady she does not drink, smoke, or have sex. She has never done anything bad to get grounded. Hell she has got grounded for not carrying groceries in (keep in mind she had no idea her mom was home or even went to the store) she is a honest person and is very shy she is also very smart. She never gets bad grades and is taking all honors and college classes in high school yet her mom still treats her this way. I wish there was a way to help her out. Any advice?