If there is an excessive amount of wiring on an LV halogen, it may drop the voltage to a level that doesn't allow the bulbs to get hot enough for the halogen cycle to work property which means that they will burn out repeatedly prematurely.

Check the voltage at the pins on the puck.

Vibration from the inside of the cabinet above the pucks also shortens bulb life.

The 12 V bulbs are not as bad as higher voltage (with 120 V bulbs being very sensitive).

I have encountered some 12 V bulbs that are not as good as they have been historically, but have not found it tied to any particular brand.

One of the reasons vehicles us lower voltage bulbs is that the filaments can be made more rugged than higher voltage bulbs.

Filaments fail more frequently on often used cabinets (vibration). It may apply in her situation.

On the problematic pucks, did the original bulbs last a reasonable amount of time, then once she replaced them, the problems started? Could the quality of the bulbs she's buying be at fault?

I have learned over the years that all halogen bulbs are not created equal. In the 90's my parents owned a kids clothes shop that was lighted by about 20 MR16 bulbs on tracks. We did experimentation with several brands of bulbs and found that the bulbs sold exclusively at electrical and lighting houses (Iwasaki, Ushio, Osram amongst others) lasted a LOT longer than those bought at big box stores. The ones sold in multiple blister packs were pure crap.

I would imagine that the situation only got worse today.

From the information I have, it seems that the frequent lamp failures are limited to individual pucks. As I said, the lights were installed ten years ago although I don't know exactly how long she's been having the problem.

I'll have to give her a call and get more information.