Mrs. Bennet found, with amazement and horror, that her husband would not advance a guinea to buy clothes for his daughter. He protested that she should receive from him no mark of affection whatever on the occasion. Mrs. Bennet could hardly comprehend it. That his anger could be carried to such a point of inconceivable resentment as to refuse his daughter a privilege without which her marriage would scarcely seem valid, exceeded all that she could believe possible. She was more alive to the disgrace which the want of new clothes must reflect on her daughter's nuptials, than to any sense of shame at her eloping and living with Wickham a fortnight before they took place. ch 50

How important was it for a bride to get new clothes on her wedding? Was it a recent or long established trend? Did the wedding clothes include the bridal gown and trousseau or was it just the trousseau?

Given that it is Mrs. Bennet who bemoans the loss of this bridal custom, I am not sure how important it really was.