I read that there is often a triggering event, or perhaps exposure/stress that gets the latent breast cancer to become invasive. Is that true?

By trigger event we mean an accident, some injury to the breast or other event. When breast cancer is diagnosed soon after that, it is really more related to the timing of seeing a doctor for the stressful event. The breast cancer just happens to be found by medical examination at the same time. There's probably not any biological reason that altered the rate of breast cancer development. There is data that suggests the immunosuppression related to stress can be a factor in cancer development. But having a stressful event per se will not cause a woman's breast cancer to suddenly become invasive.
I think cancer development is so much more complicated than a stressful life event might indicate. The most recent studies looking at stress and breast cancer occurrence have indicated no connection. In other words, although minimizing stress in your life is good for other reasons, stress does not seem to be a contributing factor to breast cancer recurring.