Do you care about albums? If not its easy to merge all the photos from multiple libraries. Let me repeat that, following this method will not preserve the albums from one of your libraries. Ok, lets go.
Determine which library will be your primary library, this lucky library WILL be able to preserve its albums. (In your case, probably your wife's library, your daughter will just have to recreate her albums)
If you have an external drive: Copy this primary library onto the external HDD, Get Info on the external and enable Ignore Permissions on the drive. Reference: http://support.apple.com/kb/HT1198
If you don't have an external drive: Make copies of both iPhoto libraries in the /Users/Shared/ folder. Use chmod or finder to change permissions for all users to read and write to these libraries and apply to contents. i.e.
sudo chmod -R 777 Example_iPhotoLib
Open your primary library with iPhoto. Find the secondary library in Finder, right click and chose "Show Package Contents". Look for a folder called 'Masters', or possibly 'Originals' depending on your version of iPhoto. Drag this folder onto the open iPhoto window and all photos should start to import, thereby merging and duplicating all photos from the secondary library into your primary library.
Clean up by deleting unnecessary or duplicate iPhoto libraries. Always have a backup.