Single AA might be a bit large for keychaining, but knowing ladies and their purses, she might have enough space for it. I personally like the EagleTac D25A mini's size a lot for that purpose, and the Titanium version can still be found. The interface could be too complicated initially, so otherwise the Thrunite Ti firefly model could be a nice alternative.
Small footnote: non-flashaholics don't normally value the use of a moonlight mode, so might initially prefer the 60/3 model.
Another option could be the Fenix E05 or E01. Very unexciting lights, but they do what they should without offering a battery draining high lumen mode that she might never need but will still use because a light might default to that.