Mab is almost certainly aware of the Many Worlds multiverse theory and that other versions of herself exist. That does not an Intellectus make.
I'm pretty sure I recently saw WoJ that Mab isn't just "aware" of the "theory," but capable of communications between alt!Mabs. That's a hell of a lot more... but still does not an Intellectus make; there would have to be some sort of shared consciousness, while the existing WoJ could mean something as fragile & laborious as an inter-universe dit-dit-dah Morse!
... her own twin sister Aurora ...
Titania, I presume you meant.
... If she can’t get on with the being most like her in the universe, she is not going to get on with a being even more like herself from another universe ...
We don't know their histories, but I suspect a love-triangle (with mortal-Mab and mortal-Titania as two corners), with their Faerie mantling happening more-or-less at the climax of the emotional debacle. Then the Mantles kept the flames smoldering & reconciliation incredibly hard; then The Oberon Affair re-igniting the blaze.
I think two cold-and-logical Mab's might each see the advantages of communications between them; the insurmountable barriers mean that none can gain advantage over the others, none can suffer a setback in their own universe, and the differing intel each can turn up can be shared by all.
Win-win for Mab.
As usual.
(indeed, this could help explain how Mab so-often seems to know so very much, even though
we never see her consulting with a spy-network)