After a ruling by Dublin's High Court, she will now be forced to return clothes that she took during their Joshua Tree tour in the 1980s.
She had claimed that the items, including a stetson hat, trousers and a sweatshirt - thought to be worth €5,000 altogether - were given to her as gifts, and that she had the right to put them up for auction at Christie's.
On ordering the return of the clothes as well as photos taken during the tour, Mr Justice Michael Peart said that Cashman's inconsistency put her credibility into doubt.
Neither Cashman nor U2 were at the hearing, with the band currently on their rescheduled Pacific leg of their Vertigo world tour.