It means that your mother has a fistula-in-ano, which has two opening one on the skin around the anus & other inside the(anus) anal canal. The entire tract needs to be removed so that the soiling of undergarments with pus/mucus discharge from fistula stops.
Next Steps
Get admitted for general fitness & get her operated. Various methods/surgical procedures are available. Best is open fistulectomy sos spinceter repair.
Health Tips
Avoid constipation. drink plenty of fluids, take high fibre diet