I remain unconvinced that it was anything but a bad decision. Sure, they didn’t know WHICH specific method she would use to try and do them all harm, but they did know she was planning to do them harm somehow. Quite a few of the possibilities would have been schemes that depended on at least one party being ignorant of the danger. All of those could have been defeated by simply telling him. Plus, there’s the huge ethical concern of knowingly making an uninvolved third party a target of a murderer without his knowledge or consent. Not their finest moment, IMO.