The universal grade item that Tanya had was called "Mirror of Tsarasa". This item allowed her to observe the fate of people or even worlds. She had some control over this item but as universal grade items were extremely hard to control, there were many times when she would see many fates that she did not want to.
Her home world was safe because Tanya regularly used this item to see the fate of her own world. This way if other worlds were planning to attack them or if some kind of disaster was about to befall her world, she would inform the powerful people of her world about it who could take preventative measures.
But the more Tanya used this item, the more fates of unknown worlds she would be able to see. If it was just seeing, then it was fine. Even though there were many cruel scenes shown to her, Tanya could just consider them as stories and then she did not have to worry too much about it.
