Urgent help needed

Hi to anyone reading this, im currently having a major issue with an item i sold to a buyer. It was a top, size large in womens. The buyer recieved the item and has flagged it as significantly not as described, stating its more a childs size or a size small. I took every photo possible of the top and the sizing, stated in the title and the description and somehow vinted has taken her side even this is a complete lie and fraudulent. Ive been orderwd to return the item or risk losing my money. There is no ppssible way she could have proved the top i sent isnt the one she recieved and there is no possible way vinted should have sided with her. Im very confused and have contacted vinted legal. Im wondering if anyone has any advice on how i go about getting my money and refusing the return as the item is exactly as described to which she has lied saying it is not. Thankyou