My girlfriend (24) is dealing with depression, and I'm feeling lost on how to support her.

I’ve been in a relationship with my girlfriend for about nine months now, and she frequently experiences depressive episodes that cause her to pull away significantly. During those times, it feels as if I no longer have a girlfriend. Because of our busy schedules, we can only meet 1-3 times a week, and sometimes not at all. I find it challenging to support her when she declines my efforts to see her and takes hours to respond to my texts. When she finally does reply, her messages are brief and lack the usual warmth, which is out of character for her. Should I consider reaching out to her parents or friends to share what’s going on? Is it appropriate to send her supportive messages even though I haven’t received a response to my last one? I genuinely want to be there for her, but it feels like she’s intentionally keeping me at a distance. It’s tough for me knowing she’s struggling and feeling helpless about how to assist her. She mentioned that she doesn’t want to discuss her feelings because it’s overwhelming, yet it’s difficult to maintain a normal conversation when I feel responsible for carrying it due to her minimal replies. I’m unsure whether I should continue to express my usual cheerful self around her or scale back my emotions so I don’t add to her stress. She rarely shares what’s bothering her, only mentioning that she’s in a “weird mood.” The decline in her mood has been gradual but worsened over the past week and a half—she initially told me her mood had dipped, but even our daily exchanges of "good morning" and "good night" have stopped. Now, I barely receive one or two texts a day, and she has turned down my attempts to see her since this started. Any advice would be greatly appreciated. I truly want to do everything I can for the person I love.