NO! Don't go in the water with it on! Seaworld gave you the wrong information. This is a $5-10,000 piece of equipment and you don't want it ruined.
2 of my 3 kids are diabetics, and they have made several friends who also are diabetic. A few have insulin pumps. The pump must be 'parked' or paused, then removed (the thin-set stays under the skin, but the tubing and pump are removed). When the swimmer gets out of the water, they have to re-attach their pump.
No one gets a pump without extensive training one-on-one with a CDE (certified diabetic educator). Have your friend call the person who trained her and get specific instructions. Some of the pumps are 'water-resistant' but that is simply to protect them from an occasional splash. NONE of them are made to be complete submersed underwater for a prolonged period of time. It wouldn't hurt for her to show one of the others traveling in your group how to take care of the pump, should she be unavailable and her son be in a situation where she cannot be there and he needs help.
Have a great time!