About frustrations with team errors...we've recently dealt with this. My daughter tries to keep her focus on her role. She is there to pitch and her teammates are there to play defense behind her. If there are errors then all she can do is try to keep doing her job and lift her teammates up. If she loses her cool then she can't do her job.
I think this is a very important point for all pitchers to understand. You just have to make the best pitch you can every pitch and then what happens will happen. The pitcher has a critical role to play, but it takes a team to win.