Only 7 weeks?? this time frame is more than enough for most people to test positive...one time exposure is considered a risk as well as you have mentioned that she refrained from any sexual activity till last december..there is a possibility..if she tested pos run the required confirmatory test like a western blot for confirmation..until confirmed she isn't poz!
All positive tests have to be confirmed by a Western Blot or a comparable approved test to confirm positive results.
Ideally the hiv test should give a results after 4-6 weeks after exposure. Has there been a confirmatory test (western blot) done?