I've seen this before. She is stressing out. Stress is caused by fear. She doesn't like the fear so she wants to get away from it and not deal with it. So, she starts walking batters, knowing that you'll eventually have to come in and take her off the mound. Do it after 2 batters and she is secretly relieved even sooner. I like the suggestion of having her face a tough lineup in practice, seeing how she reacts once runners get on and she knows she's not getting pulled. Just my opinion.