SInce updating to iOS8 my wife has only a handful of her photos on her iPad but she has her entire collection (100s) sitting happily on her iPhone.
Have both the iPhone and the iPad been updated to iOS 8? Have the 100 missing photos been taken with the iPhone? Have the missing photos been in the Photo Stream on the iPad or have they been synced to the iPad?
In any case you may want to install last night's update with the bug fixes:
iOS 8.0.2
This release contains improvements and bug fixes, including:
• Fixes an issue in iOS 8.0.1 that impacted cellular network connectivity and Touch ID on iPhone 6 and iPhone 6 Plus
• Fixes a bug so HealthKit apps can now be made available on the App Store
• Addresses an issue where 3rd party keyboards could become deselected when a user enters their passcode
• Fixes an issue that prevented some apps from accessing photos from the Photo Library
• Improves the reliability of the Reachability feature on iPhone 6 and iPhone 6 Plus
• Fixes an issue that could cause unexpected cellular data usage when receiving SMS/MMS messages
• Better support of Ask To Buy for Family Sharing for In-App Purchases
• Fixes an issue where ringtones were sometimes not restored from iCloud backups
• Fixes a bug that prevented uploading photos and videos from Safari
For information on the security content of this update, please visit this website:
http://support.apple.com/kb/HT1222