The eGear Pico in the picture below is in the same vein as the Nano, but I would echo the BOOM. The quantum has a weird battery, but recharging is simple, and it is MUCH brighter than comparably sized lights.
So many great replies. I'm going to work them. To clarify a few points. Anything with a AAA or CR2 will be to heavy. Button cells would be ok, they are readily available here and she would cope with that I imagine. They are not cheep though. By specialist I mean something that is technically difficult like the 10180 that you can ruin if you over discharge etc. Or something she can't buy herself. Those Led Lenser light claim a higher brightness than other button cell lights with that type of LED but I'm not sure I believe them Now that Nitecore Tube that looks good. But how are they getting 45L from a what looks like a little bulb style LED (as in, not a flat diode like you would fine in a more powerful light). At a guess I'd say higher voltages, defiantly work a look though, I wonder if they ship to NZ. It's just the light and maybe 3 keys, that's all she carries along with a small cell. I don't see her dropping any of the keys, so it's only the light that can change. That Inova is nice looking, not really any different than the Photon or the Spark though brightness wise is it though. She teaches teenagers, they should know not to eat batteries I'd hope Sooo it look like the Nitecore Tube is the only light option that is going be be any brighter than the others. It does look like something she would like.
I gave my kids 9V batts when they were babies... stops them from putting stuff in their mouth all the time .
You didn't specifically include it in your OP but I think the one handed operation of the Tube would be welcome. Coming out of a building at night, keys in hand, purse hanging from one arm and the other filled with books, papers, school projects, whatever. Not the time to be working a twisty.
I hate to say it, but I wouldn't trust anything running on coin cells to be bright enough to navigate stairs, in the dark, in urban conditions. Short of a complete blackout, I suppose.
And even more to support the Tube I'm starting to wonder how I've never heard of this little light before.
I have an Iain Sinclair Eon Extreme Floodlight. Two XML's powered by a li-poly battery (thin and rectangular). The tint is a crisp white and its a real 300 lumens on high. No keychain attachment tho. Hopefully the Tube is just a small version with a decent tint. Time will tell but it looks cool on paper.
I know I'm late to the party but I saw that nobody mentioned the Photon Rex. I've got a couple and think that output wise it compares well to the Tube (I only have that video above to judge from) but I don't remember if the UI was as good. They've been sitting virtually unused since I got them and don't seem to be taking a charge any more. To be fair I think it's been 4 years or more. (They took too long to come in the mail, I ordered at AAA light and went that way instead)
Ah, correct. Didnt see that below the big printed price they still list them at on their web site. I wonder what happens with the lifetime warranty? Edit. They're still selling the little magnetic charging harness and the usb/solar charging kit...