Western Meadow is a melanistic miniature kangaskhan that was abandoned by her pack at an early age and taken care of mostly and fended off by herself. Being melanistic or albino is a taboo unlike shinies and being refused resources at a young age developmental years made it difficult to grow.

Wes is growing like inch by inch though you don't see it unless you're physically making a mark on a wall. She's just not hitting that typical kanga height for her species and age. Maybe or maybe not she'll hit that massive kanga-size. 

Not many Pokemon get a read on Wes's morality