She points to the San Remo Manual on International Law Applicable to Armed Conflicts at Sea, including this section:
SECTION V : NEUTRAL MERCHANT VESSELS AND CIVIL AIRCRAFT
Neutral merchant vessels
67. Merchant vessels flying the flag of neutral States may not be attacked unless they:
(a) are believed on reasonable grounds to be carrying contraband or breaching a blockade, and after prior warning they intentionally and clearly refuse to stop, or intentionally and clearly resist visit, search or capture;Quite clearly, Section 67 (a) clearly describes the Israel/flotilla situation exactly. Read the entire article here.