Stretch Panic/WMG

The sister's inconsistent human forms are thematic.
The main page speculates that the programmers didn't care or there might be some absurdly difficult hidden challenge in picking the sister's correct forms, but here's another rationalization: each sister can be short, tall or fat, wear any kind of clothes, and she won't care because she's so obsessed with her ideal form that her true physical form just doesn't matter anymore. Each sister is so far gone in her vanity that she's completely lost her true self that nature gave her. So the randomized human forms emphasize the fact that the sisters are totally out of touch with reality and it doesn't make any difference to them what physical body they have in the real world.