Here is the fragment again:
Because Loraine had to clean up the kitchen mess left by her roommate Bob.
You correctly identified the fragment as a subordinate clause. Because, the subordinate conjunction that begins the clause, is the clue.
To fix this fragment, you could remove the subordinate conjunction. Then you would have the complete thought necessary for a main clause:
Loraine had to clean up the kitchen mess left by her roommate Bob.
Or you could use Punctuation Rule 1:
Main Clause + Ø + Subordinate Clause.
The correction would look like this:
Loraine was really angry
because she had to clean up the kitchen mess left by
her roommate Bob.
Or you could use Punctuation Rule 2:
Subordinate Clause + , + Main Clause.
And the correction would look like this:
Because Loraine had to clean up the kitchen mess left
by her roommate Bob,
she decided to eat his last cupcake.
Enjoy having a court jester at your disposal!