> The surprising thing is not that she was "allowed" to get married. Everyone is. The surprising thing is that someone was willing to marry her.
People marry serial killers more often that one would want to believe. Just do a search for “serial killers married in prison” and you’ll see “top-10” clickbait lists on almost every result. Some people are just crazy and idolize convicts. Someone marrying Holmes is nothing novel. Maybe they were attracted to her psychopathic personality? That happens sometimes.