It's possible that both times around the lamp itself was fine and it was just the ballast (read: control unit) that was having issues. Generally when one side flickers or works intermittently that's what is causing it. If it does happen again try swapping the lamp from one headlight to the other and see if the problem follows the lamp or stays in one place. That will determine what's actually not working properly.
HID lamps and ballasts do cost more when compared to the price of halogens, but remember that dealer prices are always
ridiculous compared to what you could spend elsewhere. Generally speaking HIDs have much longer lifetimes than halogen lamps... generally. There are of course exceptions to every rule. I've certainly gone through 4-5 halogen replacements in my car in a single year (and no I didn't touch the lamps :P). I've had my HIDs in for two years without issue. Something to keep in mind is that HIDs don't like being turned on and off quickly frequently. Similar to fluorescent lights they have a warm up period, and flipping them on and off will shorten the life of the components. So certainly something to let your daughter know if she turns them on and off a whole lot. If she does it's better to let them warm up (about five seconds or so) before turning them back off again.
As to how much better HIDs are than halogens...... it doesn't seem like a lot when you're just looking at them, however it's a huge difference when put side by side with halogens, as they do put out 3x as much light. In a similar situation I borrowed a friend's car that had dynamic HIDs..... basically they turned as you turned to light around corners. It didn't really seem like a helpful feature until I stopped driving it and drove my car again and realized I couldn't see around corners anymore!
things you can do to improve the lighting, and especially get away from crazy dealer prices. First I'd recommend going with a pair of Phillips 85122+ lamps... they're arguably the best D2S lamps on the market. You can get them from places like thetretofitsource
for $95/pair, and those are unused straight from the factory in Germany, not an ebay knock off. You can also buy any number of ballasts to drive a D2S lamp..... TRS sells a number of those as well, but off the top of my head I couldn't recommend one over the other. If you want more details on that I'd recommend spending a little time on HiDplanet
to learn more than you ever wished to know about HID components. Granted at this point your extended warranty is covering things via your deductible so I'm not suggesting you go out and spend a bunch of money right now, just suggesting things for the future. If you did end up replacing the ballasts you could swap over to 55w ballasts vs. the stock 35w ones..... way more light output. Lastly you could swap in clear lenses to replace the stock fresnel ones in the OEM HID housings. You wouldn't think it would make much difference, but it really really