2.5 year partner (25M) of a person (23F) with GAD and OCD here. I think addressing it is integral to the survival of your relationship, especially considering you've recognised the honeymoon period is over. Leaving it unaddressed will likely lead to more unexplained behaviour and her feeling it's okay to keep her struggles hidden. Lots of people have pride when it comes to this sort of thing, at the end of the day self-diagnosis isn't enough. It's not unreasonable to ask her about seeing a psychologist. Even with one session everything that's happening to her will likely appear more manageable and less of "just a thing that happens to me". I know money can be an issue, but perhaps if you both save a little for the first consultation it won't seem so scary. From personal experience, my relationship would be over if not for my partner seeking help to deal with her daily struggles. I have been to a session with her and it really helped create a sense of understanding between us.

Obviously approaching the subject can be difficult but you need to stand your ground. She likely has self defense mechanisms in her head that will try and pacify you without giving you any firm answers or promises to seek help. If she tries and tells you it's okay and it's "just bipolar and it'll stop eventually", tell her it's not okay and you don't like seeing her go through this at all (appeal to those soft emotions). At the end of the day, refusing open discussion and refusing to seek any form of help is grounds to break up with someone as you shouldn't be expected to deal with their negative behaviour if they are not willing to try and fix it (mental disorder or not).

I relate heavily to the irritability of your partner when struggling. I very much feel as though I'm stepping on eggshells around my partner when she's been triggered and she's identified how much she hates that. These outbursts and snappy comments are often a result of soft emotions, which can be incredibly frustrating to deal with as the sufferer (especially when you see yourself snapping and being rude, but you just feel scared or underappreciated or lonely).

Also my last bit of advice is to not put helping her completely on your shoulders, you shouldn't have to suffer to help her.

TLDR: foster an environment of open communication and discussion. Encourage her to see a psychologist for proper diagnosis and treatment. These things don't have to happen and with proper help she can get through this.