Do I pay extra tax for an inherited IRA?

I inherited 1/2 of an IRA from my mom, who passed away in 2016. The other half went to my dad. She had taken her required distribution before she passed away.

It was not a lot of money and I cashed it out, but from my Turbo Tax entry it looks like I am being charged a lot in taxes even though it doesn't add that much to my 2016 income. How do I enter this into my income and is it usual to be charged so much in tax for a small inheritance amount?