Two or three Ls of water/day isn't enough. It's too cheap and too multi-purpose to skimp there. If she cuts her hand, she could use at least half that just cleaning the wound. And you know she isn't going to want to go two weeks w/o washing a dish or taking a bird-bath.

A rain collection barrel is a good idea. If the need arises, the park will likely lift the ban temporarily. They don't have to be large barrels -- two smaller containers (like 20-gal/75 L) tubs or totes, nested and filled with supplies would be less bulky. Provide the screening/netting/cover.

Food - if she's got water and cooking ability, add some quick-cook foods. The type of scenario you're anticipating is likely to be a PITA, she needs some sense of normalcy and something to focus on.

Gift her with one of those clip-on toilet seat/lids from a sporting goods store and a matching large plastic bucket. They're cheap for the value involved when the need arises. Make sure she understands the need to keep the NEW plastic bucket out of the sun. Maybe pack it with supplies so she doesn't use it outdoors.

Chaos is right on target with his advice about flashlights.

Sue