Panel 1: We start off with Elly taking Mike and Lizzie to the Costume Corner.
Panel 2: Something has captured Mike's interest.
Panel 3: We next see him point to a display of masks.
Panels 4-6 As he tries on clown, goblin and witch masks, Lizzie laughs in delight.
Panel 7: As Elly looks at pumpkins she can carve into a jack-o-lantern and Mike tries on a monster mask, Lizzie's gleeful giggles capture the attention of a senior citizen.
Panel 8: She comes up and says Hello....
Panel 9:....and Lizzie howls in terror.
Summary: Since Lizzie is one of the freakish children that populate Retconland, she knows the difference between a kid in a mask and someone's real face. Since Random Lady was both real and 'hideous', she's terrified. In the real world, she'd probably have giggled.