Depression Support Group
Depression is a real and debilitating condition that is often misunderstood by family and friends. Its meaning can range from a prolonged period of sadness to an actual mental illness with specific symptoms. Find and share experiences with others who are going through the same struggles.
If not it's time for her to get off your case.
But she won't. My big sister is this child. I am the golden child. I am not sure that helped me much, because mum spent years intensely haranging me while she sent my sister to coventry for this crime or that. I think the sister got the best deal...
Anyway my big sis can't do anything right. It's some severe mental illness on the part of my mum. The only thing you can do, is grow up, get your education, and get the firetruck out of dodge.
Get away from her. Form your identity away from her. Then come back, the new you, strong, safe, protected - and if she treats you like a 2nd class citizen? Tell her off. you'll have the strength then, and by strength I mean money, ability to just walk out, ability to make it alone.
By all means, start to remove your mother's approval from your sense of well being. It sounds like she gives and withdraws approval very quickly.