Actually the medication itself is OTC, but the strength is not. The infraction of this 'crime' would be minor, even if she did have it on her. 'Prescription' ibuprofen is anything above 200mg in a single dose (so 400mg, 600mg, and 800mg). Taking 4 tablets at once of the over-the-counter ibuprofen is the exact same as taking 1 tablet of 800mg 'prescription' ibuprofen.
While professionally and personally I do not condone the sharing of prescription medications, I find that the reason the higher doses of ibuprofen are prescription-only is so people do not take high-doses of ibuprofen (also naproxen and aspirin, although aspirin is frowned-upon in the medical community). High doses of NSAIDs (ibuprofen, naproxen, aspirin, just to name a few) can cause stomach bleeds, acid reflux, stomach ulcers, and (less importantly) thin the blood excessively. These are important issues that need the attention of a medical professional's monitoring - it was just today that I had a patient tell me that she was admitted to the hospital 20 years ago for taking too much aspirin and had a stomach ulcer occur (not suicide-related overdose).
Waste not, get your budget cut next year.