Dealership (non Renault) issues - advice

looking for some wisdom.... My gf bought a 3yr old approved used Golf mk6 in March from a VW main dealer.

It has been in and out since 3 weeks after she bought it with a "rattle/ bang" in the drivers door which seems to be more prevalent on sunny days.. 9 + visits and numerous fault finds and fixes and it still isn't fixed 6 months later!

What are her options - (aside from me shouting louder at them) ?