Asking on behalf of gf

Took the jeep into a Dodge dealership for 1200 dollar fix (replaced oil cooler, cleaned engine, replaced upper and lower intake gaskets, topped off coolant and changed oil, cleaned off under side of jeep it was covered in oil). The mechanic noted this could have been caused the previous oil change.

Jiffy Lube was responsible for the previous oil change. After communicating this with Jiffy Lube they said she could be reimbursed for the entire amount. A representative of Jiffy Lube said she could come in and a check would be ready. She goes in and the manager says they were not responsible and will not reimburse her.

Is there a way to prove they are responsible? Also, for them to have said a check was ready makes me think this manager is goal keeping.

Anyone have any input/ lived experiences that are similar? ty