Beats me. Maybe "she acted in a good cause" or "she did it for a good reason." Maybe "she did it because it was the right thing to do."
JohnGardne7 is correct. "In service of (the) Good" means she did it for a good cause, as opposed to "in the service/name of Evil. I personally think 'Good' should be treated as a proper noun in the English translation.
The translation provided is nonsense. The essence of the Norwegian sentence can be stated as, "She did it for the common good."
this translates to english badly - it should something like 'she acted for a good cause' or 'she acted in good faith'