A bottle of water is heavy and bulky, so I wouldn't expect anyone to carry one unless they expected to use it.

The photon is another matter. All I can think of is to emphasis the non-emergency uses. I use my LEDs several times a week, just casually. A small knife is used even more often, for opening packages and doing my nails. The other core device is a whistle. Would it help to present it as a rape/mugging alarm? I reckon a hard blast on a fox-40 would give most rapists pause for thought. Even if she never gets to blow it (and I hope she never does), just having it can be a comfort sometimes; reduces the feeling of helplessness eg if she is alone and there is someone she isn't quite sure of.

The other cunning ploy is to turn it into jewelrey. I am pretty sure you can get attractive silver whistles on neck-chains. I doubt you can get one with integral blade and LED, but I could be wrong or maybe you could have it custom made. Don't be too ambitious. Any little thing could help.

Does she carry a mobile phone? They often have backlights strong enough to see by. Better than nothing anyway, if it's pitch dark. The trick is to know and remember to get it out and use it when the time comes.

Information may be the best thing you can give her. She can't leave that at home. Even if she dismisses it when you talk to her, there's a chance it will be there in her head when she needs it.