I had sepsis - was at the doctors with my daughter because she was getting some results back - I collapsed in the surgery. Taken to hospital and found out my gallbladder had started to 'putrify'. I'd had gallbladder attacks for years and GP had said that gallbladder was better in than out. So I put up with the attacks.
The surgeon said that the operation to remove it was a 'bloody mess', had to convert to an 'open' procedure and it had also affected my pancreas - this still bothers me from time to time. I was in hospital for three nights until I discharged myself because I couldn't sleep because of various reasons. I made a quick recovery at home.
My son developed sepsis after a hernia operation.
GP was refusing a home visit the following week (4th day after surgery) - he couldn't walk because of pain and his wound was leaking foul liquid.
My husband got me to stand in the back of his van with my son and delivered us to the doctors. (Good use of caravan steps.). There was no way he could lower himself in and out of a car.
We were stood either side of him, holding him up, in reception when his wound burst open and dropped about half a pint of foul liquid on the floor.
He was seen immediately after that - ambulance straight to hospital. Emergency operation and a much longer stay in hospital than his original day case hernia operation. He had a problem with low blood pressure for a while afterwards but made a good recovery.
Also, last year, my six week premature granddaughter had sepsis in NICU after major abdominal surgery - was touch and go for a while but she pulled through. She was only 2lb in weight at that point. Interestingly, my daughter did not know her baby had sepsis until baby was discharged six weeks later. It was on the discharge letter. When she asked why she wasn't told, they said because it was a very common occurrence and there was no point worrying her. She wasn't told that her baby also had a collapsed lung - that's another story.
What I'm trying to say is that we panic when we hear 'sepsis' but it's quite common and easily treated.
I wish your SIL a speedy recovery.