Hey there!!
I think what was so unhelpful to me, is when my family starts judging me, and they actually don't know that I have depression, they might as well don't know what it is and I understand, but they keep arriving to conclusions by saying "Oh I know exactly what you're going through, it's just the laziness!!". That is more than enough to put me down even more, and gives me absolutely no hope, because they don't want to listen to me completely, they think I'm hiding something while I'm not, and because of that, I gave up on talking, and depression is becoming more severe everyday, and now, both my family and I are not doing well, but if they listen, and stop throwing stuff that are absolutely not true and stop holding onto them, we both will live a better life, and they don't have to be concerned.
A huge part of helping depressed people is by letting them talk, and you have to listen until they unload it out completely, because part of depression is anger, depressed people are definitely angry with themselves, angry with those who don't seem to understand.
What you need to do to also stay unaffected by her depression, is to simply let her unload the negativity, let her wash it off her brain, and then she'll hopefully feel better, and you'll feel better too!! If she's alone by herself, go to her with a smile on your face, let her know you're here for her, and tell her that you want her to talk. And, for me, I like unloading when someone is hugging me or when my head is on someone's shoulder. If you do that, you will feel that you have the power to make things right, and you'll gain confidence, and she will feel protected. Just try not to leave her sitting alone, because depression makes you talk to yourself non-stop, fueling the brain with more anger and more hopelessness, not until she speaks her mind tot the person she loves!!
I hope that I didn't misunderstand something, or that I wasn't helpful.
Take care