If your a real U16 player who moved up to U18 and now the coach is adding real college players are your chances at being seen by college coaches hurt?
Loaded question!... but I agree, it's a very good question.
1. In general if your team is playing at larger exposure tournaments where they have a 16u division (and also at nationals) you would expect to see more D1 coaches looking there as opposed to 18u. So I think moving to 18u could impact your daughter's looks more than the college player. D2 and NAIA schools, however, might be recruiting both equally.
2. The BEST way for your DD to be seen by a college coach is for her to have contacted the school and sent an email expressing her interest along with a game schedule. I can think of no reason why a coach would opt to not come look at your daughter (assuming she is at the right events) based on the fact that her team is picking up a few college players.
3. Having a college player on a team shouldn't affect your daughter's looks any more than that team having a committed (signed or verbaled) player which many 16u and 18u teams have. Obviously the more committed players you have on a team the less chance coaches are going to spend a lot of time passively watching that team, but again ... most coaches who are going to recruit your daughter are there because she wrote them, not because they randomly decided to watch her team play.
4. Most college players are there to stay sharp over the off-season. They are not interested in coming onto a team and taking all of the innings away from anyone. It was our experience last year (on an 18u team with college and committed players) that when a coach was present to watch an unrecruited player, the committed players were more than happy to step aside and let her shine. Clearly the coach and players should lay that expectation down from day 1, but on most teams I think it is understood.
Best of luck to your daughter this season!