I don't think it's going to be Sharpe. Coleen Wing's mother already works for the Hand. Deviating from the source material so that Foggy's mom is also not only a member of the Hand but the Snakeroot itself? That's way too much of a stretch, particularly since Foggy isn't a fighter of any sort.
And I'm not sure if she's Sunset Bain either since Bain is an Iron Man villain but that's actually a really good guess. She's fought a number of other heroes in the Marvel U like Machine Man, Ghost Rider and Taskmaster. She's a weapons manufacturer so she could have ties with Justin Hammer and Diamondback. The Hand have ties to a number of corporations like Roxxon. There's nothing saying that Sunset Bain can't be made CEO of IGH or that IGH can't be a subsidiary of Baintronics. And Sunset Bain is absolutely amoral enough to want to get involved in the creation of supersoldiers and would join The Hand if it meant more power.
But let's look at who the villain is likely to be and what role Weaver's character is likely to play in the story. Stick's narration in the trailer, the big hand in the logo, The Hand having Elektra's body and the lingering subplot of The Hand digging a hole in New York City all but confirms that she's somehow related to them in some sort of leadership position. She could very well be The Beast but he needs a human host and that doesn't bring us any closer to Weaver's character's name.
Now let's look at what role this character (whoever she is) is likely to play in bringing the heroes together. Daredevil is already an enemy of The Hand. Colleen Wing's mother is named Izuma Ozawa and she's connected the The Hand so that brings the two of them together. (Considering that Sigourney Weaver can't pass for Japanese, she's probably a separate character.) And if Iron Fist sticks to the source material, Danny is going to be framed for the murder of Harold Meachum by a ninja. And that ninja is likely to be working for The Hand.
Luke is likely to be brought in by Matt as he helps to clear Luke's name. But that says nothing about Jessica getting involved since Luke and Jessica left on poor terms and Danny and Jessica could meet through Hogarth but Jessica and Hogarth are also not currently the best of friends. That means that Jessica needs a connection to Matt... or the villain needs a connection to IGH. We know that Seagate Prison was contracting somebody else to do their experiments on inmates. We have no idea if Burnstein was working for IGH or somebody else but considering how we only know of three organizations in the MCU building supersoldiers and AIM nor HYDRA is tied to any of the Netflix series so far (and I don't buy that Momentum Alternative Energy isn't tied to somebody bigger), it's likely that Burnstein was an employee of IGH and that's going to get Luke to want to make amends with Jessica since he knows that she's investigating them. Therefore it follows that Weaver's character is involved with both groups.
Weaver is too old to be Typhoid Mary and Mary is way too unstable to lead any sort of organization. Ma Gnucci is a shady underworld type who may make deals with The Hand but I can't see her leading IGH. I don't think that she's Viper due to rights issues with Fox and the fact that HYDRA would be a third villain faction to add to what's already a convoluted story.
The part that makes me think that she isn't Bain is that there's another female villain who's a gangster, billionaire corporate executive and has an army of ninjas at her disposal. More importantly, the only Defender who lacks a personal reason to get involved is Misty Knight. Sigourney Weaver is clearly Celia Ricadonna. In the comics, she's an enemy of Misty's who played a role in both a Daughters of the Dragon miniseries and the post-Civil War Heroes for Hire ongoing. She also clearly has some skill with black magick where she can pull weapons out of thin air despite them not being holstered on her which leads back to The Hand every bit as much as the ninja thing. Then there's also the whole, "unbreakable katana" thing. I'd be surprised if that wasn't Weaver's character.
