The months is the only acceptable guidelines for a conclusive negative result.
If you don't know the difference between the inside of a vagina with a condom and the inside of a vagina without one, you've got some serious issues down there.
1) Too soon for ARS
2) IF she had HIV - 1 in 2000
3) Only if you really think you didn't have a condom on. Test at 6 weeks to see if you have HIV or not, 12 weeks if you want a Teak/FDA/CDC seal of approval.