In ch. 4 of Heinlein's Have Space Suit, Will Travel, two flying saucers land in the field behind the protagonist Kip's house. Two figures come out of one. We later learn that these are the Mother Thing, followed by Peewee. The scene is depicted on the cover of the Del Rey paperback, which can be found by web searching.
In this scene, why is Peewee wearing a space suit?
In the remainder of the chapter, Peewee brings Kip up to speed on the situation he's gotten himself into, but there are interruptions, and Kip spends a lot of time expressing disbelief. During this time, Peewee describes landing the flying saucer with coaching from the Mother Thing. But there never seems to be any explanation of why she'd be wearing a space suit.