Hmm, it's hard to say without reading it. But one way is to make her click with the other character in a different way. Or make him complex, interesting, and sympathetic too.
Or maybe to have there be some very strong reason why she "should" be with the other guy besides her feelings for this one. A prior promise? They're married in a culture where marriages can't just be dissolved? Family pressure? Cultural similarities? They've shared something very important in the past?
Love triangles are tough, because (unless you allow for polyamory) someone's going to get hurt, and there's the potential for readers getting miffed if the character they like best is the one who's tossed over. So the ultimate choice often is painfully obvious, because the author makes the "other" man or woman one dimensional or unsympathetic. Or the writer makes him or her noble, then kills the person off (sometimes in an act of self sacrifice).
One possible way around is to make one of the two people change in some way that makes them and the person drift away from one another. I read a series recently where the author did this, though it felt a bit contrived.