How to deal with emotionally unstable girlfriend?

My girlfriend is and has been emotionally unstable ever since starting birth control (note she’s now off it for 2 months). She’ll be normal some days then sometimes she’ll start an argument over something very small like me using a different cup than the one she got me for a week... Something like that. I’m trying to figure out how I can help or improve the situation.

Like I spend prob 70% of all my free time with her and she then turns around and says to me that I don’t think she’s a priority in my life. Which is assuming things about me that just aren’t even close to true but her mind is telling her they are. I don't know how I can convince her otherwise because I’ve already been trying so hard and I don't know what else to do.
How to deal with emotionally unstable girlfriend?
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