What to tell my daughter?

My daughter is 4 and I told her I was going to the doctor and that I would see her the next day.  She didn't even question it   My mother came to stay at our house for a week and she brought my daughter to the hospital the day after surgery.  She was fine.  She didn't even ask about my IV, Catheter or anything.  She wanted to play with the TV buttons on my bed and of course the call nurse buttons.