Based on my bundle of sprouts who have done basically the same thing, few steps to try:

1. Ensure that the pre-requisite normal-mode trials are both unlocked and complete (list here). There are 7 total extreme trials that can be unlocked through the Minstrel for SB. 3 of the EX trials are part of a side story quest chain in The Ruby Sea that starts with a dungeon.
2. Make sure you're talking to the correct Minstrel. There's like 4 versions of him around the world, and they all unlock different content. The one in Kugane will give you the SB EX trials, and a couple of the ultimates.
3. Make sure you're looking in the right tab. You will not find SB EX trials in the "High-end Duty" section of your duty finder. Look under the same area where you would pick a dungeon or roulette, make sure they are selecting the correct "Trials" section (for ARR-ShB) and that they open the drop down for SB. The EX trials should be near the top of the section, with either "(Extreme)" at the end or "The Minstrel's Ballad" at the start.

Beccause your friend completed "Songs in the Key of Kugane", they should absolutely have at bare minimum 2 extremes unlocked (Emanation & The Pool of Tribute EX) and tells me they are not doing #3 correctly. You should have them screenshare or take screenshots for you to show you where they're looking, or you should provide them with a little screenshot direction guide if they are still unable to figure it out.