Braking a bad habit

Our nine-year-old daughter uses the restroom as a calm-down spot and often just a place to escape from responsibilities and work.
When I tell her to do something, she often answers, “I need to use the restroom first.” She wakes up at night two or three times, and she starts walking to the restroom, half asleep. And because she doesn’t get to sleep straight through the night, she has a lot of headaches. She is an early riser also, and I feel like she doesn’t get enough sleep.
She has done this since she was little.
We went to the doctor a few years ago, and they said that this was a habit and nothing was wrong with her that she would need to go.
After doing the TSG course, I realized that she has difficulty accepting a no answer, so going to the restroom is her way of not following an instruction immediately. Also, she tends to push us away, so she may go there to escape from us and not take part in the family activities.
I think a quiet time in the middle of the day would help her. She loves reading. Do you think it is a good idea to put on her schedule thirty minutes of reading in private twice a day? And tell her to consider this her calm down time and personal time? And talk with her to give up hiding in the restroom so often because it wastes her time.
She might say that she needs to go, and she knows her body better than me. How do I explain that this is a bad habit and her mind is tricking her?
Thank you very much for your help and guidance.