Because it upsets you Not to be horrible but when they can sense they've pushed a button they'll do it again... heck we do it as adults! Don't take it personally she LOVES you and it's her way of deflecting the issue. Definitely a smart cookie, and not the only child to do it I assure you

Just acknowledge that she misses her daddy, and tell her that you do too but unfortunately if daddy was here he would say you need to do xyz too.