When I am depressed, sometimes I don't want to talk about it to anybody either. I suspect your mother on some level, at least, wants to blame herself--and that's what you are picking up on.
Some people, also, want to blame us when we are depressed, as if it's something we can totally control without help. That would lead me not to admit to it......
Are you able to talk about it with a mental-health professional or some other kind of counselor?
Remember that depression can be caused by a chemical problem in the brain and/or it can even be a normal reaction to life circumstances.