Harry, who had been watching an England rugby game on TV, gave 23-year-old Lindsay Swagerty his towel, which she kept as a souvenir. He also took her for drinks at the California hotel the following evening, where the party drank beer and shots.
Ms Swagerty told the Sun: "Someone got the idea everyone should jump into the pool. This guy picked me up and jumped in with me in his arms - high heels and all.
"Harry was the first to notice me when I got out and he wrapped his towel around me to keep me warm. It was such a gentlemanly thing to do. He is probably the most charming man I'll ever meet."
Harry, who is in the US for Apache helicopter training, has been seen visiting local San Diego haunts including a local bar with four friends from the British Army Air Corps.