I am not sure what you mean by "suddenly becomes active"
Chronic HBV sufferers tend not to have "flair ups of symptoms unless they develop another unrelated disorder. Chronic HBV sufferers tend to have varying degrees of nausea, loss of appetite, yellowish skin etc or maybr none of these. So, what do you mean by "suddenly becomes active?"
Well, active or not, it does mean that she can transmit the disease to you via blood to blood transmission and also through sexual activity. If she becomes pregnant, she can also transmit the disease to the foetus. I am still not sure what you mean by her virus has suddenly bbecome active.