So, a bit of context.

I'm 20 and am in an LTR with a girl that's 18. We've been in a LTR for about 2 months. She's submissive and does whatever I want. I lost my virginity to her and all around she is a pretty sweet girl. While I was gaming her, she had these 'outburst' of sadness where she would get emotional and say some depressing things. I pretty much acted the way TRP said, I told her how I will be there for her, trying my best to be her rock. It works great so far, she submits to me and treats me as somebody with higher SMV than her.

When it comes to her emotions, she told me how she will often feel sad for no reason, she says it started in elementary, IMO I just think it's PMS and classic mood swings women have. She often tells me she wishes she had my positive outlook on life. She pretty much bases this on the fact of how much I make her laugh and how unfazed by things I seem. I try to follow Stoic teachings and my life motto if you wanna call it that is:" Actions don't upset me, my beliefs tho." This has helped me to always focus on myself and take responsibility.

We were talking over the phone tonight and she said she got her period today. I'm mentioning this because maybe that's the reason why everything happened, but... As we were talking she all of the sudden became really quiet, so I assumed she was sleepy. Then she told me how she feels sad and she told me how she got a number of a psychiatrist and she wants to see him because of the sadness she feels. I asked her if there is a reason for the way she feels and she said:" It honestly doesn't exist one, I just feel sad for no reason." and then she broke down crying saying how she thinks she is worthless and how she is a disappointment to everyone in her life etc. I didn't wanna play Dr. House and try do diagnose her so I Just said that if there is no reason she should visit a psychiatrist and that I will be here for her if she wants to talk about anything. We eventually hung up and here I am...

So what is my question?

What the fuck do I do?

I don't wanna leave her because she hasn't shown me any red flags and I can tell that being with me makes her feel happy. I told her multiple times about the way I deal with emotions but as a women she will always be controlled by them. I don't wanna give her any advice because I've never been in her shoes, I went pretty quickly through my high school emo phase and realized that it's a waste of fucking time, so I can't relate to what she is going through.

So, what can I do?