If she always used a condom she can't have hiv. Condoms don't have micro tears or pinhole leaks either and only the head needs protection, so that is why the condom is always safe sex.
If you doubt her word about her past usage of a condom, you can take a duo after 4 weeks for a conclusive result.
KayFa92,
From what you have written, I do not see any reason to doubt her. I think her test is likely accurate. If her last sexual encounter was months ago and knowing that HIV 1/2 Ab, p24 (4th gen) test is accurate in 95% of cases after 4 weeks, then her test is accurate. Besides, if she always had protected sex, she was not at risk to begin with.
Also, remember that most people do not have HIV and though we obsess about it, majority of the people we encounter are not infected with HIV, having said that, it is better to always practice safe sex.
All the best.