Rest assured, your sister's next surgery will be a breeze compared to the j-pouch surgery. Essentially, it's just closing the ileostomy, so surgical pain is minimal in comparison. Some people get a lot of gas pain during the weeks following, and this can be quite overwhelming. But, you can help prevent this by walking a lot, getting off opiates as soon as feasible, and small frequent meals.
The other main issue is serious diarrhea as the pouch and small intestine adapt to being a reservoir. She has a bit of a head start with so much time since her colectomy. The barriers she was told about amount to diaper rash ointments. Prevention of anal irritation and excoriation is far better than trying to treat it after it happens.
By all means, encourage your sister to become a member here, so she can ask questions as they come up. Plus, she won't feel so alone. This is a place where she can speak plainly and no one will become alarmed or offended. Believe me, we've heard it all before, and most of us have had similar experiences. She can also read the forums without registering too!
Good for you for being such a kind person to your sister!
Jan 