I find Nidalee confusing, as she can change from form to form so freely it almost seems like she was made for Vastaya, but her diluted blood separates her from them? Did she just have the gene and it can just activate if encouraged to do so, like some messed up recessive gene or is she some sort of Human that changed into Vastaya through magical ways? Can someone clear this up for me?
Vastaya come from a union of humans and a race of spiritual shapeshiftery dudes known as the vastayashai'rei, so vastaya can interbreed with humans, though it dilutes the inherent magic that comes with being a vastaya since there's even more human in there now than before. The power comes from their heritage.
The vastaya tree has a small part where it lists "shapeshifters",which isn't connected to the tree anymore. http://am-a.akamaihd.net/image?f=http://universe-meeps.leagueoflegends.com/v1/assets/images/vastaya-tree-en_us.jpg&resize=1400:
It likely refers to people like Nidalee or the swine-guy from the story. They have vastayan blood,but are regular humans who have the ability to change into an animal-shape.
Meanwhile the vastaya are magical beings,who need magic to survive and who are animal-like in their regular form,with the ability to modify their forms to some extend.
