She lived for a number of years after the surgeries.

Very sorry to hear about your SIL. Unless she has other issues or complications, she can live a normal life if she wishes. Keep an eye on her mental state.

and below the knee prosthetics are a bit easier to deal with than above the knee prosthetics are.

Coma is good at this point. I can't imagine the kind of pain she must have been ignoring to get that much bowel deterioration.

She is going to need a lot of support if she manages to come out of this. These are two huge changes to deal with.

Some people find the ostomy the most distressing, here's how to find a support group and yes, they will visit her in the hospital and rehab: https://www.ostomy.org/support-group-finder/ I can vouch for them, they are very good.

Most of the amputees I dealt with were at the VA, which has its own support network, but I did find this for civilians: https://www.amputee-coalition.org/support-groups-peer-support/support-group-network/

my mom was an amputee she was a refugee during World War II and was forced to walk for miles and miles in the Bavarian Mountains as a 10 year old. That gave her frost bite and 14 years later when she was pregnant with me, the hormones in her body caused the leg to become gangrenous. She had to have it amputated with local anesthetic in order to save her fetus. She was 23 and probably in better shape that my sister in law at 64.