bowl movement

My daughter is now 17years of age she has been toilet trained since she was 4. She has never had any issues going to the bathroom.She has had a few accidents in the past while on the a transportation bus. Not reaching home in time. But other then that she really  hasn't had any issues in that department.In the past two weeks she has had two
bowl movements while taking a bath the odd thing about this is that it concerns me because she will just lay there with no concern of what she just did. She  has never done this while living with us. She now resides at a residential  program at the Evergreen School  located in Milford Mass.  She has behavior problems she is autistic. The Staff there
tells us that she never had a bowl movement while in her bath, But she  has done this on two occasion while we are we are visiting.I she her 4 times a week, and we try bringing her home on some weekends depending on her mood. I feel their must be a reason why she is doing this.