How do I recover lost photos from iCloud. They are not in recently deleted

Did your sister try logging into iCloud.com to check whether there are some deleted pictures? Use the Apple ID and Passwords to login the website to get it.

If you can't get it from the iCloud.com and the "recently deleted", it's hard to find them back unless you've ever created an iPhone backup. You know the photos that you don't sync to iCloud can be saved to iTunes Backup or iCloud backup. Just restore your device will bring them all back.

If the photo's that are trying to be recovered are taken on a different device make sure iCloud photos are turned on in settings:

On your iPhone, iPad, or iPod touch:

Go to Settings > [your name] > iCloud.

Tap Photos.

Turn on iCloud Photos.

On your Mac:

Go to System Preferences > iCloud.

Next to Photos, click Options.

Select iCloud Photos. After you turn on iCloud Photos, you might need to connect to Wi-Fi and wait a few minutes. Then look for your photos again.

Shown below:

From Get help with missing photos

Make sure that you are also signed in with the same Apple ID.

Unhide your photos:

On your iPhone, iPad, or iPod touch:

Open the Photos app and go to the Albums tab.

Tap Hidden under Other Albums.

Select the photo or video that you want to unhide.

Tap share icon > Unhide.

On your Mac:

Open Photos and in the menu bar, click View > Show Hidden Photo Album.

In the left sidebar, select Hidden.

Select the photo or video that you want to unhide.

Control-click the photo, then choose Unhide Photo. You can also choose Image > Unhide Photo from the menu bar, or press Command-L.

If you use iCloud Photos, the photos that you hide on one device are hidden on your other devices too.