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 wanted to fix it this way:
Sandra spent every dime on her vacation to Cancun, Mexico, where she went
shopping, dancing, swimming, and sightseeing,
nevertheless,
she does not care that her rent will be late or that she will have
to eat macaroni and cheese for a month.
A comma splice occurs when you have two complete sentences joined with just a comma. Sandra spent every dime on her vacation ... begins the first sentence. She does not care ... starts the second sentence.
The addition of the conjunctive adverb nevertheless doesn't alter the fact that you still have two complete sentences joined with a comma alone.
You might want to consult the rules for fixing comma splices and fused sentences.