Because her mom would make her take it back.
or
Mt Rushmore. They're a rock group.. it's a rock...group
or
Three. One to climb the ladder while the second kicks the ladder out from under her. And the third to say, "I knew that was too high for you dear."
or
Twenty. One to hold the bulb, two to turn the ladder, and 17 to be on the guest list.
or
"Let me see your birth certificate".
or