Answer:
No, the court should not hold in favor of Huckleberry.
Explanation:
The rule of mitigation that Huckleberry tries to use in her favor states that the non-breaching party (Butterfield) should have taken all the necessary steps to reduce her loss, e.g. take a job in New York. She probably argued that Butterfield leaving for England to meet with her children made things worse.
But in this case, Butterfield relied on Huckleberry's promise to organize her life and the well being of her children. Butterfield made a lot of changes and sacrifices in her life because of this, e.g. forfeiting unpaid alimony, transferring custody of her children , etc.
Moving to a different city or country requires a lot of work, expat life is not easy and not everyone can handle it. Butterfield took decisions that affected the lives of many people and she is not responsible for Huckleberry's breaching, the only party responsible for all this mess is Huckleberry and it is normal that Butterfield would want to go to where her children are.