To see if your HDD is full, select the HDD drive, then press the Display button. If the 515 is on a digital channel, ignore the 1st screen and press Display again until there's a bar of icons at top and a Time remaining section in bottom right. That TR section will show how many hours:min of HDD capacity is left at the currently selected rec mode.
If your HDD shows 0 hours:min, you need to Delete titles. I fill one of my machines up all the time (to use all the bits on the HDD), then use the HDD Menu > Delete all titles options. You can also delete one or Multiple titles by clicking the Title button, then click OK on a title and select one of the Delete options.
If your HDD isn't full, let us know since that might require more troubleshooting.
Be aware that, with the 515 or a FW updated 2160A or 513, you can pre-title your wife's timer rec program so each recorded title has not only the index pic, but a title, day of week, date and time, as described here: