Enlarged fibroid uteri can cause constipation and in fact, pressure symptoms (constipation, urinary symptoms) are one reason for removing enlarged fibroid uteri. How large was the uterus (measured between pubis and umbilicus)?
I do not know whether the large uterus was the cause of her constipation. Most probably it was "idiopathic". As to the colonic perforation- in the presence of hard stools it would be defined as stercoral perforation.