I would say that the "payoff" is not there in any endurance sport - triathalons, track, running, swimming, etc. Not that some individuals cannot make some money off of it - but in general, it is not football, baseball, basketball, etc. The best endurance athletes would be hard pressed to ever make the money of the worst football player or basketball player. So, overall, I think any notion of a monetary reward in relation to the decision is simply not there.
As for college scholarships - if that is a priority for her - I think she could easily do triathlons through HS, swim and still get a D-I scholarship for running almost anywhere she wanted. . . .. .If that is what she wants.
It is high school. Sports are games. If she likes one game better than another game - do what makes you happy. Sounds like she is doing what she enjoys and has aspirations for - hard to argue against that.
All of that being said - as a coach - it would sure be a little depressing to know that someone with that ability had chosen another sport - even if she is really good at the other. So, from a coaching perspective - it would be a bit of a downer for sure.