Its True that Time Stop would affect Altair, but that's as far as it goes. Coming near her would Erase the very concept of Kars itself due to her existence Erasing invisible Forcefields
https://imgur.com/a/WAHgs
Universe Erasure is useless considering she has resistence to Existence Erasure from beings from her own tier on top of EoS Altair Erasing the Universe and Recreating another one casually
Merger Sponges from D4C is also useless via her Mid-Godly Regen and BTD isn't helpful against an Acausal being in a neutral battlefield.
Her power null isn't the same as GER's Zero Reset Willpower Dropping or an average basic power null. It literally erases every plot twists and powerups from a character and returns them back to their weakest state. I don't see how TWU being an Acausal or Kars duplicates help considering she can Erase them all along with the entire Universe.
And the reason why "copy and use her own abilities against her" isn't helpful is because she already fought and defeated someone who possessed the exact same abilities as her and were much more superior to her.
As for how Altair can beat Kars:
She can Erase or Warp the Entire Universe along with Kars and his duplicates instantly
Use Representation Exposition to revise the plot of Kars aka reformat his existence with a thought
Outline Origin Kars back to Part 2 Pillar men form
Use her Probability Manipulation+Possession (Which worked on an Acausal being) to possess Kars
Factor Mimic and copies all his abilities or bring his own version of Kars to fight him. But let's give you the benefit of the doubt and say Kars absorbs copy Kars.
She can use Existence Change to overwrite Kars's Concept and take over his existence.