WHATEVER she has done, whether she has remorse, whether she's a psychopath all of the is irrelevant as far as I am concerned. She should be treated in the way any other British citizen is.
If there are mechanisms for bringing British citizens to trial for what they have done overseas, then use them.
If there are mechanisms for assessing and managing any risk to the public, then use them.
The fact that she may or may not have had eligibility for another citizenship - never taken up by her, or by her parents on her behalf as a child - should not be used to make a second-class tier of British citizenship.
As a PP has pointed out, Israel offers Israeli citizenship to anyone Jewish. So anyone who is British and Jewish has access to another citizenship. Presumably that gives the government the right to strip them of citizenship in the same way, no matter whether they have any connection to Israel, no matter how many generations their family has been British citizens.
Anyone with Irish parents or grandparents? They have the right to Irish citizenship.