I'd suggest that you try running CM11 on an external SD card first to see if you/she like the custom ROM enough before you decide to flash it into the HD+ internal memory to replace the stock ROM.
The instruction on how to create a SD-based CM10.x image can be found at
http://forum.xda-developers.com/show...#post36421852; the latest set of files corresponding to CM11 can be found at
http://forum.xda-developers.com/show....php?t=2600572 (see the links labeled cm-11-20141129-UNOFFICIAL-ovation-sdcard.zip & initial sdcard image for ovation), plus you'd need a Gapps zip file from
http://wiki.cyanogenmod.org/w/Google_Apps.
Instructions for flashing CM into HD+ internal memory can be found at
http://forum.xda-developers.com/show....php?t=2317500 and
http://forum.xda-developers.com/show....php?t=2679899.
If your HD+ is one of those units that do not seem to be able to boot into an SD card, see
http://forum.xda-developers.com/show....php?t=2288688.