She is incorrect. If this money was taken out of her separate property investment account (prior to marriage) and then placed into a joint account with you during marriage and that money was used or accrued interest during marriage, there is nothing you owe her. That account will be divided according to your state's marital asset and debt distribution laws (so either equitable distribution or community property, depending on what law your state follows). In Wisconsin, your state follows equitable distribution laws. So, depending on what is equitable and fair, the account will be separated accordingly. If that account made money or funds used from it made money in investments, I would argue she commingled the funds and therefore that account was a marital asset and not a separate property asset.