Originally, after Poddy escaped her kidnappers with the Venusian, she was supposed to die from the explosion that occured. The Venusian would live, protected by her body. Her uncle would then blame everything on her parents for not paying attention to their children as they grew up. The editor insisted that this was a children's novel and the main character simply could not die. The new ending is the one we all know- she is injured by the blast and ends up in the hospital. Her uncle still reams out her parents, but he says he thinks their daughter will turn out okay, but he doesn't know about Clark. Clark overhears this and doesn't understand, because his sister is the one who is hurt. I'm not sure which ending I prefer.
This information came from Grumbles from the Grave. If you want more details, go buy it. It also has large amounts of correspondence between Heinlein and his agents and/or editors over the years, and many of his own comments. It was published after his death by the permission of his widow.
Both endings are included in the newest version of "Podkayne". You can decide for yourself which one you prefer.
