You will lose 25 quid if you cancel before I think the 9th May. I would try for an East Pass in the resale using whoever is travelling with you's registration and take the hit.
This is her only French festival date... which means she obviously is doing others fests', so why not if she's still in Europe in August (I know some people here asked for her)
im upset that the black friday sale the airline I was looking at put everything onsale EXCEPT the route I was taking. So now I hope Cyber Monday or Travel Tuesday has a deal or else I just pay ( a fair ) price instead of maybe saving a couple hundred on airfare. If you advertise everythings going on sale then do it.