1099-R and how to handle it

My sister passed away last year, leaving her retirement money in her account in the amount of $26K.  In her Will she had requested that as her executor,  I contribute 1/2 of that money to a couple of charities she designated, which I did in 2019.  That means that 13K was contributed as charitable donations and 13K was mine to keep.  However, I received a 1099-R in my name in the amount of $26K which from the IRS perspective means, I believe, that I'm responsible for taxes on that amount since the total amount was signed over to me personally by her Credit Union where the account was held.  Claiming the contributed $13K  as a deduction doesn't reduce my taxes hardly at all!  What is the best way to handle this so that I'm not having to pay taxes on $26K.  I'm happy to pay taxes on the $13K, but not the full $26K if it's at all possible.