Upgrading the OS does not upgrade iPhoto. So, make a back up and upgrade your OS.
Most Simple Back Up
Drag the iPhoto Library from your Pictures Folder to another Disk. This will make a copy on that disk.
Slightly more complex:
Use an app that will do incremental back ups. This is a very good way to work. The first time you run the back up the app will make a complete copy of the Library. Thereafter it will update the back up with the changes you have made. That makes subsequent back ups much faster. Many of these apps also have scheduling capabilities: So set it up and it will do the back up automatically. Examples of such apps: Chronosync or DejaVu . But are many others. Search on MacUpdate
Thanks Terence, I wasn't sure if iPhoto upgraded itself in that path - it feels like 10 years since I was on Leopard - but forgot to mention that I'll have her upgrade iPhoto as well (to iLife '11) in this process.
I was going to just have her do a TM volume backup, then also drag copy her Home folder to the other new volume. That would also pick up all her other files as well as the iPhoto library, no?
I use Carbon Copy Cloner myself, and also Chronosync occasionally (different reasons). Super Duper is another good one.