Winnie's words to the toad on page 15 are as follows: "It'd be better if I could be like you, out in the open and making up my own mind." Winnie is speaking to the toad in an attempt to express her own feelings. She feels trapped by her life, her community, and her family. She wants to be able to make her own decisions and to travel and see the world.
What Winnie learns after this encounter, once she has had time to interact with the Tucks, is that freedom isn't all it is cracked up to be. The Tucks are actually sad at being as 'free' as they are, and wish there were limits on their life. Winnie benefits from their experience and chooses a mortal life as a result, although she does convey immortality onto the toad.