Your wife can log into the App Store using your Apple I.D. and download Pages 5.2 for free.
The sole requirement is that she has upgraded her Mac to OSX 10.9.2 Mavericks.
She does not need to uninstall Pages '09. The App Store will move that to a subfolder: Applications/iWork
Deleting Pages '09 is a bad idea because Pages 5 and the new Numbers and Keynote are all downgrades, not upgrades. In the case of Pages 5 it is missing 100 features and very buggy.
You can actually work with both applications on your Mac, just be aware of which file is opening in which application.
If she has 4.3 and Mavericks, she's elegible for free 5.2.
Have her log into her Mac App Store account with her Apple ID and Purchase the Pages app. It should be free.
If you and she both are on the same account name, then use that common name when you log into the Mac App Store on her computer. Go to the Purchases tab, find Pages and click Download.