As to IBD being always fatal - be careful of who you claim has their facts wrong - it's possible for boas to be asymptomatic carriers of IBD - perhaps for their entire lives. I was the owner of two long terms carriers - one who exhibited symptoms and one who was an asymptomatic carrier for in excess of 6 years. After discussing the disease with the good folks at UCD, I was flat out told that it was possible that the asymptomatic one could have remained so for another 6 years or perhaps her entire life.
Fact is, no one knows if it's 100% fatal in boa constrictors.
As for 70% of boas carrying IBD - again no one knows the true rate of occurence. The testing is invasive and inaccurate and so few people actually pay for histopathology that the true rate of occurrence is unknown. However, per the Merck Veterinary manual, up to 50% of boas tested are carriers.
Per this link - up to 33% of necropsied boas were carriers:
https://netfiles.uiuc.edu/doortiz2/www/IBD.pdf
I've covered this ground on this forum before and there were a lot of wedged panties in a lot of butt cracks. When it comes to IBD, throw out what you think you know and read from the people who are actually researching it and the folks who are treating and testing their animals for it.
To the OP: what should your friend do? Talk to a vet who actually treats the disease, a lab who diagnoses it or see if one of the researchers like Jacobson will answer some queries. There is too much flat out bad information floating around about this disease for her to get a decent answer on any forum.