she is paying her Chanel couture suit for sure, a person in Condenast handle her payment. For the gown she wears to Met, i think it should be sponsored by Chanel. Considering her position at that event, Chanel would love to treat her as a house ambassador, especially not many celebrities choose Chanel at red carpet, cause the brand refuses to pay.
Her dressing allowance is around 200K annually reported a few years ago
But u know, Her long-term boyfriend is billionaire, so regardless of her salary and allowance, she can afford couture anyway