Upgrade an iMac? - Need Advice

[JoeM]

My sis has an iMac Core 2 Duo 2.8 GHz (2008) with the standard 2 GB RAM which she uses with Adobe CS 6 for mostly Photoshop and InDesign work with Suitcase 6. She says it's very slow and was wondering if she can get enough of a performance improvement by adding more RAM (4GB to bring it to the max of 6 GB) or if she should start saving to buy a new Mac.

Any thoughts or advice from iMac users? TIA