Schemes of the Lich King
The Elf Queen is mystically connected to every elf, and so every elf is mystically connected to every other elf.
Generally, elves find it an honor to work as an agent of the Elf Queen, while non-elves consider it something of a miracle.
All elves, whether they are Shadow Elves, Dark Elves, Wood Elves, etc., find they have a certain amount of alliance to the Elf Queen. The High Druid is either figuratively or literally the Elf Queen’s half-sister.