Am I wrong to be upset about this?

My mom died between Christmas and new years. I lived 800 miles away, so most of the time, I can pretend she is still there, then occasionally, I am overcome by grief.
She died sooner than she expected, and had a little money that she split between her children, asking us to give half to her designated charities so we could get the tax deduction.
I was assigned to give the money to the foundation at her Church.
Last month the money was wire transferred to our accounts.
In my mourning, and denial, I have not yet written the check. It feels like to do so would be to admit she’s gone and I’m not ready to do that. I cry just at the thought.
My sister has been there for our mom for the last 20 years. Since I didn’t live there, I visited when I could and helped by providing mom with a monthly check ($350) that helped her not have to worry about the extras like cable and her seniors trips.
Today my sister sent my brother and I this email:
.......,Not sure if you have sent the chairity checks to him yet, but if you did he has not yet recieved them so I wanted to let you know in case they never got there and you need to stop payment.  That is such a large amount it makes me a bit nervous if it was not sent certified mail.
 
If you haven’t yet sent it, you may want to send certified or cashiers check instead of a personal check.
 
Love you…....

I don’t know if I am more upset at my sister for checking up on me, or the pastor for discussing it with her. I really don’t want to get into a family drama, but if I just stuff this hurt it will consume me.
Am I wrong?