Jerry/BTC have addressed this exact question. Their version of events is that Houlihan was with a group of BTC runners when she was first notified of her positive test and she told them about it at that time. Then, Houlihan spoke with Jerry, her lawyer, and others who asked them all to keep quiet. So, the athletes who were present at the time knew of the positive test immediately. Those who were not present did not. It's unclear who was in which group, but it's not surprising that Infeld was not, as she has been away from the rest of the team much of the time and doesn't appear to be close with Houlihan socially.
To me, the biggest unanswered question is still why the Athletics Integrity Unit did not immediately disclose the positive test and resulting suspension, as they typically do when an athlete appeals an atypical finding. Was the AIU forced to stay quiet, and if so, by who? Did Nike pressure the AIU and, if so, did they also pressure the BTC's other athletes who were aware of the positive test and suspension? Why did the BTC lie about Houlihan's status for so long?
Eventually, news of the positive test leaked from someone, as Gault was made aware and asked around. Who leaked that news and why? Houlihan mysteriously pulled out of various races that she was not, as it turns out, allowed to compete in. Were USATF aware of the suspension? What was the purpose of all this mystery? It must have put a lot of stress on the individuals involved, even if they believe Houlihan is innocent. If the AIU had followed their typical protocol, there would have been no secrets to keep.