Solution to leg cramps

I’m hoping that someone may be able to help me solve a problem. My wife is a talented triathlete, winning her age group (55-59) in several major triathlons over the past two years. She has signed up to do a full ironman distance (2.4 mile swim, 112 mile bike, 26.2 mile run) in Wisconsin but she can't seem to swim past 1200-1400 meters before she gets leg cramps. She has consulted local swim coaches, tried all their suggestions and nothing works. It's a real problem and she is thinking of giving up on the race. Since she is 57 this may be her last shot at doing something she’s wanted to do for years. She has tried hydrating (with water and tonic water), stretching, had her technique evaluated for mechanics, etc. has anyone else had this problem and if so, what the solution? I’m desperate to help her but don’t know where else to turn. If you know of anyone who might be able to help, please let me know. Thank you. Bruce