If, by contrast, a Jewish male enters into relations with a gentile woman, when he does so intentionally, she should be executed. She is executed because she caused a Jew to be involved in an unseemly transgression, as [is the law with regard to] an animal. [This applies regardless of] whether the gentile women was a minor of three years of age, or an adult, whether she was single or married. And it applies even if [the Jew] was a minor of nine years old, [she is executed].
This [punishment] is explicitly mentioned in the Torah, as [Numbers 31:16-17] states: “Behold they were [involved] with the children of Israel according to the advice of Balaam. Execute any woman fit to know a man through lying with a male.”
Rabbi Gordon on intimacy with 3 year old girls