My wife has pretty severe anxiety and at the moment it's treated fairly well, but not great, and it's been hard on us throughout the years. Your girlfriend should be going to therapy and seeing a psychiatrist about medication. There's no shame or anything wrong with medicating anxiety, it can be a debilitating, frustrating, hurtful physiological/psychological condition. My wife used to feel shame for taking medication for psychological/physiological conditions, and I thought that was so silly because these days almost everybody takes something for something... Like, my thyroid gland doesn't work and so I take synthetic thyroxine and I'll be on it for the rest of my life. There's nothing different from my thyroid not producing the right chemicals than some other organ, like the brain, producing an imbalanced set of chemicals, and if someone like me can live a normal pain free life because of synthetic lab made thyroxine, there's nothing wrong with someone else being enabled to live a normal life through something like Affexor or other anxiety and depression medication.
Throughout the years my wife has said some incredibly mean, mean things to me, and then what's also hard is the rebound from that, when she feels so guilty that it continues to overwhelm her, so I basically have to build someone back up who just spent the last 4-8 hours tearing me down. It's exhausting and difficult. Her anxiety and corresponding depression has been pretty well treated for the last 5 years, and she's has a productive life, is a great mother, good friend, good at her job, and she's a very well adjusted member of society. Without that medication though, I think that the anxiety would overwhelm her in nearly all of these areas and she'd be very destructive to herself or the relationships she's made.
Prior to her anxiety being treated well, it was over-treated and she basically had a medically induce manic depressive personality. That was a disaster, she lost a lot of friends and damaged a lot of relationships in that time. I think if I was a less patient person or someone who acted more decisively, I would have left her during that time. Thank god her psychiatrist or therapist got that prescription normalized and reduced, because it was horrible. Whoever that doctor was was complete quack.
Your girlfriend needs to seek treatment because it's unfair on the people around her if she doesn't. If she doesn't get treatment, you're not her savior and you need to be willing to walk away and let her live with the consequences of her actions. You've only been together for six months, your focus should squarely be on you, and if your partner isn't willing to put in the work to improve and uses you as this sort of bungee cord (e.g., she jumps off knowing that you'll pull her back up), then it's not healthy for either of you.