I don't think that Allomancy is the way it was done, because we are explicitly told that Bleeder could only access one Allomantic of Feurechemical ability at a time, via her single spike. Seeing as how we only see her using one ability at a time, and the addition of an second spike played such an critical role in the story, I don't find it likely that emotional Allomancy was involved. Maybe she'd gotten a hold of Lerasium, but if so, why didn't she use more abilities than one? That being said, perhaps the strongest evidence that something like that could be happening is that Bleeder only seems to be able to communicate with Wax while their in close proximity, possibly in visible range, both at the party, in the square, etc. This is similar to the limitations that we've seen from emotional (and other forms of) Allomancy.
Lumping the ability into the metal spike is the easiest answer, but also seems like it could be a bit too convenient for me.
Note: edited to remove spoiler tags. Here's to being new on the forums!