Am I liable for anything regarding the exchange of products for money between me and my relative, considering that I swore to exchange a product for a product with her, and she agreed then refused the product and took money instead, and I do not know if the money is equal to the value of the product?

If your relative did not accept the gift you gave her, even though you swore to her that she should accept it, then you have broken your oath and an expiation for breaking an oath (kaffarat yamin) is incumbent upon you. The money you paid her does not take the place of the gift, and whether the money was equal to, less than, or more than the value of the gift, you do not fulfill your oath by her acceptance of the money, unless your intention behind the oath was to reciprocate her gift and not to accept it without compensation. This is determined by your intention and the context in which you made the oath, for intentions and motives are considered in oaths. Ibn al-Qayyim said: "Indeed, intention affects an oath by specifying and generalizing it, and the reason takes its place when it is absent, and indicates it, thus affecting what it affects." It is preferable to give the expiation for the oath as a precaution and to absolve oneself of responsibility.