Thanks bjs229 and birdastrompgman for replying.
I installed rom toolbox, went to the management section, and found flash recovery. Hurray! It gives me a selection of TWRP and CWR versions to choose from. Since I rooted using WUG's root toolkit that used TWRP, I selected the latest version of TWRP? Does it matter?
I then went to Management/Backups and found the same backup I had seen there before flashing the recovery. It is listed as
teamwin backup Feb 27, 2013 08:17:46
which must be something that I did when I rooted the nexus, maybe the unrooted stock rom.
Thank you guys. Sorry for being stupid at this but this is all new territory to me. I read "Nexus 7 for dummies" but it does not get into this stuff.
Is there anything else I need to do? Do I now create a new nandroid backup using the WUG root toolkit?