Take a look at the sentence again:
The problem occurs between trouble and just. Cindy's mumbling often gets her in trouble is a main clause, so it can stand alone as a complete sentence. Just the other day, in fact, her stylist misunderstood ... begins the next complete sentence. Because these two parts have only blank space between them, they make a fused sentence, a major sentence error.
To fix the problem, you could put a period after trouble and then capitalize the J for just.