In the previous episode of 'Charmed', we learned a lot more about Abigael. She was masquerading as the demon overlord to overcome the patriarchy in the demon world, and that she is Alastair Caine's daughter, making her a half-sister to Parker and Hunter.
At this point, the Charmed Ones do not trust Abigael -- there were too many instances where she tried to doublecross Macy the first time we saw her. By the last episode, Macy got smart enough to stop trusting her, but Abigael tells her that they have more in common than Macy realizes.
Though both Macy and Abigael are half-demon, half-witch, the reasons for them being so are different. Abigael was born of a demon father and a witch mother, whereas, Macy, a half-human and half-witch, was stillborn, leading her mother to seek the help of a necromancer to bring her back to life. The necromancer used a demon's blood and so far, the show has not revealed who that demon was.
We think that it could be important to know who Macy's demon blood comes from, and it could very well be Alastair. Much like Voldemort in the 'Harry Potter' series created Horcruxes in a bid to remain immortal, the demon supplying his blood to bring back dead people could have the same motive.
The fact that both Macy's and Abigael's demon powers are the same supports this theory. Both of them have the power of pyrokinesis, though Abigael is able to control her power much more. They also have telekinesis in common, though Abigael tells her that her extreme intellect was the reason she was able to master that power so quickly.
We also don't know anything about the Vera-Vaughn sisters' extended family and though Abigael may not be related to the Vera-Vaughns, we might learn more about this extended family in the future.
'Charmed' airs on The CW on Friday nights.