This is the Photoshop forum, you really should ask questions about Elements 11 here : http://forums.adobe.com/community/photoshop_elements
That being said, I think you should be able to update Camera RAW to make it work with your D7100. Here's is a link I found using Google : http://blogs.adobe.com/pselements/adobe-camera-raw-7-4-is-now-available-for-photoshop-elem ents-11/
This is not the Photoshop forum, it is the Camera Raw forum. Your camera requires Camera Raw 7.4 or later. I don't know what versions of Camera Raw will work with Photoshop Elements 11. In Elements, you could try Help/update to see if that will automatically update you to the most current version available. Alternatively, you could try using the latest DNG converter with your raw files. But to upgrade to Photoshop Elements 12 just go to the Adobe product website and purchase an upgrade. You can download it and install. Adobe will e-mail you a serial number. Since you are purchasing an upgrade, the installation will look for your previous version and validate the serial number. It's a simple process to upgrade.
I don't know what versions of Camera Raw will work with Photoshop Elements 11.
According to Adobe, Elements 11 shipped with Camera Raw 7.1 and is compatible up to Camera Raw 8.0.
So, after upgrading Camera Raw to ACR 8.0 in PSE11, the OP should be OK opening D7100 Raw files with PSE11.