Podkayne of Mars belongs to the period where Heinlein was transitioning from juvenalia to his more adult books. I've always preferred Heinlein's works for younger readers, especially the ones which are transitionary, such as Tunnel in the Sky or Starship Troopers.
Readers might react to this book as if it was sexist. In some ways it is of course. I'm not sure that it was particularly sexist for its time (1963). Anyway, this is Heinlein who is not the most enlightened person of all time, and who around this time, in my opinion, was going insane. The book reminds me of Have Spacesuit Will Travel in that it has a genius younger child and a main character who is smart, but slightly better adjusted. The main character is as much the younger child Clark, who is basically a sociopath as it is the charming but shallow Podkayne.
Apparently, the publisher made Heinlein change the ending from a tragic one, to a slightly less tragic one, and this certainly changes the book and makes it worse. I'm not sure why the original ending is just not restored.
The book is actually pretty good and much more experimental in its structure than it seems to be. One of the better Heinlein novels for kids, but not by a long way, the best.