To clarify, I assume you mean that the new ability on Executioner does not proc via the follower. Eirena should still be able to equip the item regardless.
This is actually intended, and not a bug. It was something we discussed internally and came to the conclusion that it would eliminate any kind of gearing choice (and arguably, Follower choice) for players. For now, we’d like to see how Executioner gets used among player builds regardless of Follower, as the intent wasn’t for it to become a Follower-specific addition.