Is there a way to download the iphoto 9.6 update/installer for an offline upgrade? upgrading my mom's mac to yosemite - her internet connection is slow.  Would like to put the updater/installer on a USB drive.

on the apple site, there are direct downloads for older versions of iphoto, but not the latest.

I was also able to download yosemite and put it on a usb drive.  but not iphoto
You can put the new iPhoto itself on a USB drive, and just replace the file in Applications (after taking the necessary backup precautions, of course). It should work fine.

Source: My own experience, having upgraded a computer to Yosemite with the sole available wifi network having a finite amount of data.