Added to a stock account before mom died as joint owner. She passed, I sold part of it. My 1099B has cost basis on DOD. Should I be taxed at a higher rate like a spouse?

My sister and I were added as joint owners before mom died.  When she died, the stock was split evenly between my sister and I.  I sold part of mine in 2018 to pay 2017 taxes.  My 1099B from my investment portfolio is showing the cost basis on the DOD for mom.

I see where a spouse is taxed at a higher rate if they are added to an account, but don't see that a child is taxed at a higher rate.

I just want to make sure using the DOD as a cost basis is correct!