Gianbattista Valli, Chanel and others are commercial enterprises. They need to sell clothes to exist. Their workforce (coupeuses, modinettes, seretaries, etc.) needs to be paid. There is no any reason why these houses would give Charlotte Casiraghi clothes for free. It is not that she is a magnet, attracting crowds running to Valli or Chanel beause she has worn something on the Bal de la Rose...
Mademoiselle Casiraghi is in the lucky circumstances she can purchase clothes from the best brands. But when she gets her clothes for free, why not give it free to Princess Charlène? Or to Madame Carla Bruni-Sarkozy? Or to Princess Isabelle de Ligne de la Trémoïlle née Orsini? It is impossible for couture houses to give it all for free. And... imagine you buy something from Chanel or Gianbattista Valli and it has been
worn on a party by someone else... What you thought was couture is just
seondhand... No, impossible.