Each investment (stock, mutual fund, etc.) remains "inherited" until your wife sells it. Selling one of the investments does not change the status of others that she has not yet sold. If you are reporting the sale of a stock, mutual fund, or other investment that was part of the original inheritance, it is still inherited, no matter how long she has held it.
When your wife sells an investment, the money from the sale is her money. If she uses the money from the sale to buy stock, bonds, mutual funds, or other investments, the newly purchased investments are not inherited.