I wish I could chime in with some good advice... I've been where your friend is at. My now 10 year old gelding is a chronic colicker and has been over the course of 4 years. He colickes usually 2-3 times a year, with last year being is worst averaging once a month from december 2013 through mid summer 2014. There was once it happened twice in a matter of two weeks. He started in the fall we that we got him as a 4 1/2 year old....previous owner said he never had a history.
Vet after vet we have never been able to find a diagnosis, but rather "Well....try X this time"...only to have him colic a matter of months later. He's has gas colics, impactions, guts flipped over his spleen, other displacements, near half a dozen clinic stays with probably near $15,000 + in hospital bills alone. We've been within hours of surgery more than once. Not to mention the "piddly" emergency house calls.
We treated for ulcers (though never found any), changed his feed more than once by eliminating various things and adding probiotics...ultrasounds, scopes...you name it, he's had it done. Nothing was ever found.
However, over the years I think we've finally figured out his formula since we've been colic free for nearly a year! He is on a low sugar diet, probiotics, and a slow feeder with constant hay, and regular exercise. We'll be taking him off the spring grass soon and keeping him strictly on the slow feeder hay to see if we can get him through the spring without a colic (something that we've never been able to do).
Anyways...I guess that was an anecdotal story more so than anything. Maybe it will prompt some idea for you though. I always like to chime in on stories like this to tell people that they aren't alone!! I think with undiagnosable horses (yes, I truly believe that is a 'thing') it's almost a matter of trial and error to find the right formula that keeps them on their feet. It sounds to me as though your friend's horse may have some undiagnosed underlying issues that may be contributing too though. I do wish her all the best - repeat colickers are unbelievably stressful!!