Take a look at the original sentence again:
Sandra spent every dime on her vacation to Cancun, Mexico, where she went
shopping, dancing, swimming, and sightseeing, she
doesn't care that her rent will be late and that she will have to eat macaroni
and cheese for a week.
You chose to fix it the correct way:
Sandra spent every dime on her vacation to Cancun, Mexico, where she went
shopping, dancing, swimming, and sightseeing; she
doesn't care that her rent will be late and that she will have to eat macaroni
and cheese for a week.
Sandra spent every dime on her vacation ... starts a complete sentence. She doesn't care ... begins the second complete sentence. You are always correct when you use a semicolon between the two complete sentences that create the comma splice.