Use the "Stocks, Mutual Funds, Bonds, Other" interview to enter the sale. You'll tell TurboTax you have a 1099-B, (presumably), and identify the broker that issued it*. You'll tell TurboTax that you'll enter your sales one at a time and be dropped into the default 1099-B entry form. The you'll enter the description of the stock, the proceeds, date of sale, cost basis and date of acquisition. In the date of acquisition enter "inherited"; that will make the sale long term irrespective of how long she or the decedent actually owned the security. (That's just the way the tax law works in this area.) The basis of what was sold, typically, will be the value of the security at date of death. The broker may or may not enter the correct basis, (or not report it at all), so you may need to correct or provide that number.
The resulting gain or loss will then flow to the correct spot on your income tax return.
* The broker name is entirely for your own convenience, it doesn't appear anywhere in the income tax return.
