SoccerPOP is right; if you're just trying to figure out how to get money for college, soccer and any sport is NOT the way to do it. The way to do that is to do well in school and earn academic money because there is a hundred times more academic financial aid available than there will ever be athletic.
And again, you can make whatever you want of soccer; whether it's playing at the highest level because you think it's fun, but won't go for it, or if you're playing Challenge League because there's not a PL team close by and you do want to play in college. You can make it work and still have a life and do a whole lot of stuff outside if you do it correctly.
Kids should play because they're having fun and enjoying it, not because it's to get money or please their parents or pad a CV.
However, you seem to want a specific answer as to what to do regarding this family member, so here's as specific as I can be:
Talk to the coaches to get an average on how many games the player will participate in throughout the season. Then sit down with the child and lay it out for them and be clear about approximately how many games will be played and how much work will go into playing during the year. Lay out continued expectations regarding grades and responsibilities that continue despite the playing time--and not in a mean or scary way that intends to frighten them into a decision either.
Then ask the PLAYER what SHE wants to do and let her do it.
If she's U18, it sounds like she's probably a senior. It may be her last year to hang out with fellow players and teammates and play this competitively and it's a year she should enjoy as much as possible while still working hard. She's almost an adult; almost out of the home and having to take care of herself at college. I think she's probably ready to sit down and decide whether or not this CESA team is one SHE wants to play for, not one her family thinks she should.
