That was apparently her nickname in highschool, because of her intensity as a point guard. I think we should check with her friends, particularly her old boyfriends, whether that was the real reason. I'm not suggesting any specific meaning to that nickname, I'm just wondering what "Sarah Barracuda" would have implied at my school.
Etymological diversion: Nickname is one of those words that got divided wrongly because of the a/an of the indefinite article in English. (Another would be a naeddre, a snake, which became an adder by the reverse type of split.) It was an eke-name, meaning an also-name. "Eke" meaning also is related to "eke" as in "eke out a living." The earlier verb eacan meant "increase."
I don't know where "barracuda" comes from, though. It sounds like a Spanish corruption of a native word.