Whatever you do, you'd better back up those photos someplace because if there's a glitch, even a temporary one, her pix could be gone. You can plug each iPhone into your computer and read each as a drive. Use a photo wizard (Windows or Mac) to copy the pix from the iPhone to your computer. I did this when preparing to upgrade from my iPhone 4 to present iPhone 5. I named the folder that I created the date of the action. It doesn't matter what you call the file as long as you know what it contains.
Your main concern at this point is to safeguard/preserve the older pix that are located on the older iPhone without endangering the newer pix on the iPhone 5.