Mmy unfiled return has reported the cost basis for stock bought in 2006, but I inherited the stock owned solely by her when she pasted away in 2010.

[dascorrAZ]

it was my wife's stock

[KrisD15]

If it was solely your wife's stock, and you inherited it, your basis would be the value on the date of her passing. 

NOTE- If the stock was purchased with community funds while you lived in a community property state, you would only step-up half the basis. 

If the stock was her property exclusively, then you step-up the full value to the 2010 value.