My friend has three boys who were constantly clogging the toilet - she ended up replacing all of her toilets with industrial strength toilets!!
If she is not complaining of any stomach pain or pain in her rectum then this is just her "normal." Everyone is different and this is just her normal size, there is nothing wrong with that. You should not subject her to laxatives or a liquid diet when there are no problems. However, if she starts having problems then you should make an appointment with her doctor. If you are very concerned about this problem you can talk about this with a doctor.