Why would you worry about having said or done anything wrong? Of course you've told her that you are willing to listen.

What are "episodes" that she is having? Of course you've told her that you cannot help find solutions if she's not talking about things.

19 is an age in my experience and numerous discussions with friends that is rife with emotional turmoil as it's a complicated age for many in formulating identity and independence. It is the final teenage year albeit an adult. That's not science that's just social chit chat, to be honest. Haven't met a woman yet that would choose that exact age to revisit. I'm certain I could be proven "wrong" for voicing it, but it's not about to be proven wrong within my social circle of many.

Hope you and your gf can sort through this.