The “Elven Spell Songs” section on page 142 indicates that they are “less like skills and more like individual spells”, and thus they do not completely follow the standard rules for skills but follow them in some ways.
Further down, the list of specific rules indicates that (i) no FoRKs are possible and (ii) help dice can only come from elves with the same song or the Song of Songs but doesn’t state either way whether they can be offered as help to another.
Back in the dim and distant past when I was professionally lawyering, the rules of statutory interpretation in England and Wales included the rule that where a statute highlights a few traits/items/&c. in a category but not all of them, the presumption is that anything not specifically mentioned follows the general case; thus, my reading is that, because the “Elven Spell Songs” list mentions FoRKing and getting help but doesn’t mention offering help, then spell songs follow the general case of providing help where it fits the narrative. However, I might have missed a clarifying statement somewhere else, and BW obviously isn’t English statute law.
To provide a specific example from the first session of the new Burning WFRP game @Mark_Watson is running: another character wanted to find a good place in the forest to set an ambush; my elf (the only one in the group) had Song of Arbors so I suggested she could ask an old tree to gain insights into suitable thickets, terrain, &c. Obviously, that could be a linked test but the cool thing is the other character’s idea to draw the enemy into the ambush so representing Song of Arbors as a help die both seemed better than diverting into a test for Song of Arbors followed by a conversation with a tree that only I could take part in, and followed Mark’s general intent that we refresh the very basics a few times before adding more of the mechanics. Rather than bring everything to a halt to deep dive every mention of spell songs in the rules, Mark ruled Song of Arbors could help this time and we’d confirm later.