Why does she need to "check her attitude ?"
What she needs to be is clear about what she wants from the game and the consequences of that.
There are people on here calling her a brat because she isn't willing to settle for second best and wants to play.
That to me is well out of order. Either she wants to play in a competitive team or she doesn't. But she isn't a brat for choosing either route.
I think it's a good life lesson. If things don't work out the way you want them to then the onus on you is to decide what you want and change them. Professional players do this all the time.
It's common in all workplaces to move if you aren't getting the career development you want, especially if it is at the expense of what you believe is a poor performer.
What's important is to set your goals, appreciate their are going to be consequences to your choices and them pursue them. Rather than settle for some stuff you don't want and that limits your opportunities in some sort of misguided belief that the collective is more important than your own personal development.
Rather than expecting her to "check her attitude" I'd be encouraging her to go out and find out whether or not she really has what it takes if that's what she wants rather than listen to the assumptions of people on the internet. No one on here knows whether she is good enough or not.
And if the try outs don't work she can always stay at the old club and be non the worse off provided she doesn't spend time talking about it.