I think it's important to start noting the difference between "Lucrezia" and "the Other."
"The Other" is, indisputably, an entity that can transfer consciousness through mechanical means. Let this sink in a bit. (See Brain Uploading, which already references GG.)
1) Who says there's only one? Referring to the plans of "the Other" should immediately evoke a response of "which the Other?" In fact, we know for a fact that there's more than one: we have the Other as she currently resides in Agatha's head, and Tanevkother.
Incidentally, does anyone know of a trope where immortality is gained through brain or mind transfer to mortal hosts? As an idea, it's tropeworthy, but Brain Uploading is the closest I could find. It's certainly generally considered as being over the Moral Event Horizon, though.
2) How can we know how old she (some clues that the Other can only possess females) is? We know she has a society of dangerous worshippers at her beck and call, at the very least. That can't happen overnight.
She may, in fact, be thousands of years old, and may have been carefully seeding Europe with revenants for millenia. She may be centuries old, and prefer using shambling zombie peasant revenants for her shock troops. She may be decades old and prefer subverting institutions from the inside and using them to further her own ends. She may, in fact, be all of these at the same time, and perfectly willing to work with herself, whatever her incarnation, to achieve her end: to rule the world! (Of course!)
What else do we know about her? Well, she's insane. First off, she was a Spark once, so that's a given. But secondly, she's got generations of other Sparks ground into her thought patterns, and that's gotta have an effect. She's also extremely sensual and physically impulsive, which is a nice contrast to Agatha, who is not. She uses voice controls (and controls her offspring's voices) to make sure that her creations obey her between incarnations. And she's a consummate actress.
This is an awesome villain. And while she may not have used a slaver wasp on Von Pinn, she sure as heck did something to her brain.
Other things to note re: general Lucreziahood
1) First, Barry came back and for some reason came back with a full distrust of Klaus Wulfenbauch... who had disappeared for years and then immediately set about ruling Europe when he got back. Given what Punch and Judy told Klaus (and good LORD I wish they'd bring those two back for some exposition), what does Barry know? What does he think he knows? After all, he did make the locket to protect Agatha, and while it hid the Spark I wouldn't be surprised if a secondary use would be blocking Lucrezia's brain-transferring machine. Most importantly, where is he? I'd suspect beyond a portal somewhere. (Why DID some of Lucrezia's priestesses turn against her, cutting off the portal access to their world? Remember how Othar subverted a Geisterdaimen...)
2) On the subject of the locket, what killed Omar Von Zinzer? People often seem to assume Moloch's conclusion was correct, but compare the third panel of http://www.girlgeniusonline.com/comic.php?date=20021122
to the fourth panel of http://www.girlgeniusonline.com/comic.php?date=20061113
, a week shy of four years later.
The inevitable conclusion? Omar was a revenant!
Is it just me, or are revenants a bit like Cylons?