(Strip Number 1294, Original Publication Date, 18 May 1988)
Panel 1: We find ourselves watching Lizzie have not an especially nice time going down the slide because it got kind of hot in the sun and she doesn't have much on to insulate her.
Panel 2: She makes a stagey gesture I've only ever seen Sylvester The Cat make when she comes to a realization.
Panel 3: She covers her sore arse when she thought-bubbles "Never go down a hot slide with shorts on."
Summary: Elizabeth is young so probably this is the first time she's been exposed (if you'll pardon the expression) to what sunlight does to metal.