The memento is a naked doll with pigtails. "Teenie" is written on its back.
Based on the name, it is most likely that this was Cheryl Heather Mason's ideal standard of beauty. Pursuit of such cultural ideals, along with her feelings of abandonment from her childhood trauma, are what led her to seek approval from her peers by her decidedly illicit lifestyle. The doll itself is found inside a cooler, which alludes to a state of being frozen, referencing Cheryl's inability to deal with Harry's death.