Q: My photos library is not an option for screensaver

Hi jbell1125,

I understand that you are unable to see the Photos Library in the screensaver pane of System Preferences. Let's see if we can sort this out. 

The first thing I would check out is to try out the steps outlined below. It would walk you through removing a plist file that would show your library in other apps across your Mac. 
 

Recreate related files

iPhoto lets other apps know what photos and movies are available by storing information in two files.

First, delete the iApps plist file, which tells other apps where your iPhoto library and other files are stored.

1. Click the Finder icon in the Dock.
2. Hold down the Option key and click the Go menu.
3. Choose Library from the Go menu.
4. In the window that appears, locate the Preferences folder.
5. In the preferences folder, locate the com.apple.iApps file. Drag this file to the Trash, then restart your computer.
6. Open and iPhoto and iTunes to regenerate this file
7. Quit iPhoto and iTunes. Then, check to see if your iPhoto images now appear in your other apps.

OS X: If you can‘t see iPhoto images in other apps
https://support.apple.com/en-us/HT203149

The main thing to notice is that the article talks about iPhoto but does go in line with Photos as well. Another note would be that the section section is specifically for iPhoto. 

Let me know if this helps.

Have a good day