Here is where you enter this sale in TurboTax:
In Income & Expenses, click show more
Scroll to Stocks, Mutual Funds, Bonds, Other and
start
Did you get a 1099-B, click no
Chose the type of investment
Click Land
Enter address, net proceeds and sale date
When you calculate the net proceeds, use value of the property on the date of your mother's death and the cost of improvements as your cost basis.