Recovering photos deleted from trash and missing from iCloud

I'm sorry. Sometimes accidents and little sisters happen. A great safety feature on the iPhone is that deleted pictures remain in the "Recently Deleted" view for 30 days before they are removed permanently. As your sister found, this safety feature can be defeated by choosing to prematurely delete pictures from the "Recently Deleted" view.  If you use iCloud Photos, then that "synchronizes" its Photos Library with the phone, so what you see on the phone is what is at iCloud. iCloud Photos doesn't keep pictures in "Recently Deleted" any longer than the phone does. So it's really important to look carefully at the Recently Deleted pictures before deleting them permanently. A good practice that I follow is to (almost) never prematurely delete pictures from Recently Deleted. That 30 days has saved me from time to time.

There is a risk anytime you share an unlocked phone with someone else. It's important to keep backups of our most important pictures and work. As you see, iCloud is not meant to be a backup-- its purpose is to synchronize pictures among different devices and sometimes to save space using "Optimize Storage."

You can see this:

         If you're missing photos or videos in the Photos app - Apple Support

Basically the above says to look in Recently Deleted and in Hidden. Be sure to check your Library thoroughly-- the pictures may not be where you expect, as dates may have changed. You can use the search field with the date or location. And remember, you can sort the Library by date captured or by date added. Also, your Library view now has filters, and you may not have your filter set to "All Items.”

Unfortunately, if you don't keep your own backups to an external drive, then there really isn't any place else to look.