Queen Loretta's thoughts have been simple. Serena was already ruined. People already hated her and were even insulting her. If she were to throw more stones, won't it only win Serena some sympathy later? In any case, there were a lot of people already willing to do the work for her.
Thus, she decided to do nothing except for sending the news to Geoffrey and of course, writing to the pope regarding the impending divorce.
Apparently, her choice of inaction has been correct. Looking back, during dinner, on the same day the news has been released, her husband, king Edward V has been so angry and most of his anger has been directed at second queen Francesca.