Hi, My Mother Is 84 Years Old And Is Suffering

Hi, my mother is 84 years old and is suffering from dementia. She is not mobile so we have to use a Hoyer lift to move her around. Five years ago she had a knee replacement that resulted in an infection in her knee. The doctors decided not to remove the knee due to her mental health. She has numerous open wounds on her knee that we clean & bandage daily. The doctors have her on continuous antibiotics.
My concern is she has mucus coming from her rectum. At first it was thick & infrequent. Now it comes out like urine daily. We keep her hydrated & fed daily with smoothies containing vegetables & fruit to combat constipation. What could cause the mucus discharge? Thank you, Sharleen