Take a look at the sentence again:
When Minori left Japan to study in the United States, she thought that she
would miss her mother's delicious home cooking, however, after her first
taste of a bacon cheeseburger, she didn't care
if she ever returned to Japan.
She didn't care is a main clause. If she ever returned to Japan is a subordinate clause. A subordinate clause is an incomplete thought which you must attach to a main clause. When a subordinate clause follows a main clause, you generally need no punctuation between the two.
Go back to the sentence to try again.