Individual responsibility is not how virus transmission during a global pandemic works. If you live in you are in the middle of the second-highest spike in COVID transmission ever. Everybody is getting this shit. She literally cannot wear a mask while having her mouth worked on, and the intersection of dentists who take your insurance, follow your personal COVID rules exactly, and have an appointment when you need it is vanishingly small. Be mad at Fauci, Trump, Biden, Pfizer, and your workplaces, not your girlfriend.
Frustration and aggravation are totally normal and acceptable, and it's good and respectful to your partner to vent here to us instead of to her directly. But I really don't think you have much of a leg to stand on for sustained indignation. You are one, possibly two, in a wave of millions of cases. This is just what's happening. Chances are you will both be OK.
Rooting for the both of you.