@thepinkdresss I'm sorry for a late response, I wanted to check what the answer was with someone who helps with MACs.
I would recommend backing up your Sims 3 folder - saves, downloads, installed contents, etc ( http://sims3.crinrict.com/en/2011/03/faq-what-files-should-i-backup.html ) - I'm not sure the exact location for MAC, but I'm sure you know where they are.
Make sure your games are registered on Origin. If you don't have them registered and you've lost the codse, see if you can find your codes in the Terminal: http://bluebellflora.com/finding-your-serial-key-using-terminal/ If they're registered, they'll appear in your My Games. Make sure you have all your games registered.
While you could uninstall just Pets entirely, it's a good idea to uninstall all games and then install and patch properly afterwards to avoid any recurrence of the error. Follow these steps: http://bluebellflora.com/how-to-do-a-clean-uninstall-and-reinstall-on-a-mac/
Once you've done that, download all your games. Do not use the discs, download them straight from Origin. Then patch the game (it may ask you to patch when you install the other games) by downloading the super patch for MAC here: http://answers.ea.com/t5/The-Sims-3/FAQ-Current-Patch-1-67-Manual-links-and-more/td-p/67858
A huge thanks to Caspinwall 🙂