Hello, Thank you for the query. You did not mention how it looks like mean like a boil etc.Anyways if your mum is getting repeated pus at knee then she should have her blood sugar level fasting and postprandial done to rule out diabetes. Secondly about diet let her eat diet which does not contain meat or eggs or something which increases body heat.So avoiding such diet for some time will be helpful. Hope this helps. Thank you.