It was the only way to end OblivAeon. If OblivAeon's goal was to shatter all realities, then the only way to stop it was to bring those realities to OblivAeon. But to do that...
After the fight with Progeny, she wasn't sure she could handle what she was about to propose. Nightmist would become, well... mist if it worked. It would require everything she had and then some to open all those portals. However, if it meant saving their world, their reality, maybe... She needed to create a reality her friends could save, even if it was one without her.