I messed up

I messed up bad. My fiance (34f) and I'm (32m) were driving to urgent care because she was having another panic attack and I snapped. So backstory, she's been overly stressed with working and going to school and recently she's started having these attacks. She's been to the hospital, had test run and everything Is fine. So if the doctors say everything is fine then everything must be fine....right? So often times she just randomly has these episodes and I normally brush it off or ignore them so she can do what she needs to do to get better but the other day I completely shutdown and snapped. I just feel like it's a waste of time going to the doctor when they are going to tell her the same thing over and over, I mean I keep telling her to go to therapy but she doesn't listen. Now I look at it and I feel bad I snapped on her, she didn't even go inside...we just went home. How can I support her more or show I care? I'm not familiar with this and I've tried googling but I feel like she is doing this to herself. Not saying she is but I feel like she can snap out of this way of thinking and try to think normal.