I would speak to the Manager and ask why they have changed her key worker for the last few works that your DD is there. Explain as you have done in your post, i.e. accidents everyday and repeat to the manager what your dd said, i.e. "I asked her if she'd been asking to use toilet and she says "I ask * (keyworker) but she says no".
Her care should not have altered because she is leaving. I would be very honest with the manager and ask her what she intends to do to improve the situation. She may not be aware of what is going on! Good luck