The fog/stream debate is a double edged sword. It PROBABLY won't matter one iota, because if she is using it she won't have time to prepare or think about it, she'll just do it and deal with the consequences. But when you talk about using it with her, think about this:
Streams are less prone to being pushed around by the wind. if you spray it into the wind, you WILL get some backsplatter at you. The disadvantage is that sprays need to hit the facial area to be most effective. Fogs are a LOT more likely to be pushed around by the wind, and you will get a LOT more back at you if you are downwind of your target. The plus side is taht you can be a lot less precise in your aim, and also if he inhales the stuff- yeah. It's wicked.
You really should order another can or two. One for carry and one or more to go play with. She shoudl practice accessing it, indexing it, spraying it and seeing how much of it gets on her when she does it, so she knows what to expect.
You also don't have a hair on your butt if you don't let her hose you down with it .