Consider therapy for your hiv phobias because the only "mistake" has been ignoring this problem which is a bit of a mental health issue for at least the last 10 months. You have had a few other fears that weren't even risks, now you are worried that her test was not valid.
The reality is she couldn't even get hiv when she used the condom before + she tested negative so that should have been an insurmountable double brick wall for your idea that she can have hiv.
So, really. If you are in a long term, monogamous relationship, the fear of unprotected sex SHOULD be less if any. This is your girlfriend. That you know. You think she secretly has HIV or is with other men? Is this rational thought or irrational? You ask "don't people lie?" Well, if you are in a relationship with someone who lies, then you shouldn't be. I think going to the hospital for food poisoning and getting an HIV test is very VERY strange. But so is GRILLING your girlfriend if she's got HIV. If you are saying she's never had unprotected sex, then she could NEVER have even gotten HIV.
If you feel so inclined, you both can go get tests TOGETHER (so she knows that YOU aren't giving HER hiv) and then you both know and start on a clean state. But if I had a significant other with an HIV phobia that couldn't just have sex like a regular person with me, I'd be out of there. After a year, you are at the point in which you either trust her or you don't.
that's kind of blunt advice. I don't think you have a worry about HIV but both of you can get tested with a 4th generation duo test in 28 days and never speak of it again or worry if you have unprotected sex.