Change the situation. Have the potential partner come in a pseudo-social situation. Removes the pressure. She doesn't need to know she's having a tryout, does she? In other words, LIE. Mercenary--true. But if she falls to pieces when she's aware that she's doing a tryout anyway, then it will perpetuate the confidence issue. So a little deception might help her out of the bad experience. Who knows, she might even forgive you... :)