OK, here's the thing to focus on as this passing moment mounts to its climax: John told Elizabeth about the affair long before he declared for the presidency. Today's brou-ha-ha is old news to them. She knew about it the whole time they were out there, displaying their marriage and family, confronting her cancer with him by her side. She decided to go out on the campaign trail with him and support him with evident conviction and at the same time try to take possession of the health care issue knowing about his affair the whole time.
Insofar as this was an act of public deception, an act of private protection, she was as much a part of it as he was. Why would she do that?
Because, like Hillary, she understands that some things are a whole lot more important than private human sex acts. What Elizabeth's complicity in John's lies says is just what Hillary's loyalty to Bill said. When serious and intelligent women get close to powerful positions where they might actually be able to do good for millions of people--they commit to a complementary version of what their cheating husbands did in the first place: they put private self-indulgence way back in second place compared to the public welfare.
Good for them. Both of them.