What Causes Severe Pain In The Ear While Swimming?

My daughter has had several sets of tubes in her ears, but not for several years. Last night she went swimming in a friend s pool, then almost immediately started complaining about her one ear hurting. When she came home this afternoon (after staying overnight with her friend) we used Auro-Dri for swimmers ear rather than the left over (and possibly old/outdated) drops from the last time she had the tubes put in. Never before has she reacted like this - crying and holding her ear in pain due to the drops. Now what should I do?