The pixie cut had its pop culture debut in Roman Holiday:
A film about a rebellious runaway princess. On Kes it clearly supports the Tinker Bell comparison and makes her look spritely while showing off her ears:
The wigs varied, starting out more poufy and layered as in the first cap (the pilot) and evolving into something simpler and straighter:
The wigs were initially used to give Kes a more elfin look, but the revert to using Lien’s own hair in part was to give Kes a more grown-up look, and in part to prevent Lien from having to always wear the Ocampan ears.Source
Kes certainly looks more ‘human’ with Lien’s hair. If she looks older it’s because the change is so drastic (more often women do the reverse and cut off their long hair to appear older). The choice to have oldest Kes (Fury) revert to the short hair makes sense as it is most recognizably Kes but I actually love the bob she has in Before and After’s future. So fun and strangely brown, following up my Tink/Pan metaphors I like to think of it as Kes taking on Wendy’s role:
Wendy grows up.
I prefer Kes’s hair when it is Jennifer’s, but I prefer Kes’s look when she’s a full on pixie.