If the HIV test results are correct, then she has been extremely lucky and staying on the edge of very low probability of sexual transmission. If interested, have a look on the statistics of transmission rates and risk factors for long term sexual relationships on the articles. Their conclusion is not 100% transmission upon a certain time, however length of sexual relationship as well as other factors do affect the probability, bearing in mind some figures are for every and each sexual action. If she is fine, start using condoms to keep her safe.
Maybe she should get re-tested.Also,when were you diagnosed hiv positive?