Check the "Bill of sale" she signed when she purchased the trailer. I can almost guarantee it said "AS IS". They are under no obligation to fix anything "No Charge".
Did you check to see if the "2014" trailer had any valid warranty left? That too would have been checked on the "bill of sale". If NO she is out of luck, and you were not any help in her getting the trailer.
If they fix anything at all it would be "good will" on their part. Maybe they might give a break on the amount charged for the repairs.
Did the salesman actually say they would make the repairs? Then we could say he may have lied. BUT! All "Bill of sales" have a disclaimer saying whatever the salesperson said was B.S. and not valid unless put in writing and signed by an authorized employee.
Nothing new. This was on our "bill of sale" contracts back in 1964 when I first got into the medical business. Companies need to protect themselves from their own sales-force. :B
