Just my tuppence as it has already been said;

A culture to find which treatment works best will save not only the snake but money in the long term.

I hope you can find a vet you can persuade your friend is trustworthy - many forums will carry recommendations from users not just ours. Find then best you can then ask her how she feels about it.

Since R.I's can be fungal, bacterial and viral they make the decision to check a no-brainer for me.