The Black Widow was a member of Colonel Fury's Defenders team stationed at Castle Doom in Latveria when they were invaded by an army of Frost Giants and other creatures who originated from Asgard. She defended the walls of the castle and played sniper for her teammates with Uru ammunition supplied by fellow member Microchip. Unfortunately Shang-Chi and Falcon were overrun by too many giants, so Widow jumped from the castle window to provide clearance so they could get back inside the castle.
Natasha was aboard the Quinjet with all the firepower that was loaded up from Doctor Doom's armory, so they could take the final fight to the Midgard Serpent himself: Jormungand. While the others used themselves as a distraction for the serpent it allowed Widow to go on a retrieval mission to find Thor's hammer, Mjolnir. While she saw the Quinjet purposely torpedo itself in a kamikaze attack on Jormungand, Natasha was found worthy to pick up Mjolnir which allowed her to become the new Goddess of Thunder. She used all the power she had acquired against the serpent and everything else from Asgard, destroying everything in her wake.
Natasha was revealed to be alive when her planet was next invaded by Ultron-1320 from a parallel world which caused a temporal paradox involving four other Earths. She was pulled through the portal to Earth-45162 along with other heroes from the different realities. Together they battled Ultron with the help of the Wasp and Goliath of this reality but couldn't overtake Ultron and his Sentinels. They then came across Ultron-1321, who was the Hank Pym from the world that Ultron was spawned from.
Pym devised a plan to keep Ultron stuck in the current reality and to send Natasha and the others to his home reality of Earth-14622 so he could make up for his mistakes. They managed pass through the rift and Natasha used her hammer to close it. Now on a barren planet with no life, the heroes carried on to become the Avengers Infinity.