Kerry,
I'm not sure what I'd do, other than what you've done already - except for alert every household in the neighborhood - along with posting a sketch of the suspect. But, I live in a defined neighborhood with an HOA; your situation may be much more difficult.
Check to see if there is some Neighborhood Watch or a local Guardian Angels chapter you might contact. If not, you can always organize/coordinate a meeting with the police department and community members to talk about safety, awareness, etc.
I suspect your daughter's school has a zero tolerance policy and anything sharper than a spoon will not be tolerated. That includes any sprays or stun guns.
Another poster suggested some defense training/skills. GREAT IDEA! There may be some low cost classes locally that are available through the NRA or similar organization.
Keep 'em safe!