Phoebe broke my heart tonight

Phoebe was laying next to me and she looked like she was in a daze, thinking about something. I said "baby, what are you thinking about?" She said "Sissy doesn't love me"... I said "what do you mean, of course she loves you"... She then said "sissy won't come home to see me" and she began to cry. Oh man, that broke my heart into a million pieces. I then told her that sissy is in heaven with Jesus and she began to cry more. I thought she was too young to understand. Guess I was wrong. So so sad... She's asleep now. I'm not sure what triggered those thoughts but now it has me wondering how long she's been thinking about her Sissy.