Even if Diamond never improves and Tennessee never improves during her time there, she will be a lottery draft choice in the WNBA and will have a long and probably All-Star career there. The WNBA can deal with individual play and to some extent is designed around it.
Geno made a comment the other day about how Stewie's scoring is limited because "we only need her to take 15 shots a night". He went on to say that if the team needed her to take 25 shots per game, she might average 40-50 points per game. While Stewie's talent is obvious to WNBA teams, Diamond might benefit (in terms of her draft position) from the greater individual exposure that she will get at Tennessee, compared to what she would have had at UConn. So her choice of schools may have some rational basis.
I sense in her a very strong desire to do things her way -- she talked in a Voepel interview about not wanting a coach who would try to change what she was doing in any major way. Geno's recent comments about Stewie suggest that she may have had similar inclinations, but (albeit with some reluctance) she was ready to be coached. Probably the same thing was true of Diana. But the tendency seems to be even stronger in Diamond, which means that it is probably a good thing that she did not accept UConn's scholarship offer.