Review the original item:
Sandra spent every dime on her vacation to Cancun, Mexico, where she went
shopping, dancing, swimming, and sightseeing,
she does not care that her rent will be late or that she will have
to eat macaroni and cheese for a month.
You chose the correct way to fix the error:
Sandra spent every dime on her vacation to Cancun, Mexico, where she went
shopping, dancing, swimming, and sightseeing;
she does not care that her rent will be late or that she will have
to eat macaroni and cheese for a month.
Sandra spent every dime on her vacation ... starts a complete sentence. She does not 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.