"The human life span is much shorter than you're used to." (3.43)
Wanda knows that humans aren't the only ones out there. She learns from her time on Earth that humans burn bright and fast. And they give a lovely light.
You never know how much time you'll have. (8.135)
Before coming to Earth, Wanda wasn't really concerned with death. Her species' existence can be prolonged indefinitely as long as there's another host to be transferred into. But once she decides to stay human, her actions hold more consequence.
"It's a big universe, and there's a lot of company out there." (21.94)
Wanda teaches the humans about all the different life forms she's encountered. However, the basic moral of this story is this: humans are the best! That's why Wanda decides to stay one. Sweet. We love a story that confirms our awesomeness.