Even if it isn't requested beforehand, it is sometimes brought up at the interview (my mom's is an example). It's good that you'll be prepared instead of the possibility of having to go in for another interview or wait for an RFE to send it in. The first one looks good. Take a death certificate if possible, or something else from the hospital/doctor explaining that this was indeed the case. Have your letter notarised. Remember, they might not even bother asking you about this, so don't be too worried.
*** El Cafe ***
N400 - NYC (Brooklyn)
March 12 2010: Sent
April 7 2010: FP done- walk-in
August 3 2010: ID decision not made
December 12 2010: Lawsuit filed under 8 USC 1447(b)
March 31 2011: 31 Oath date
April 1 2011: Passport applied, picked up!