In Fang Yu's calculations, Mo Li needed about a week or two to come back. However, she wasn't sure if he would really come back after two weeks or just continue training Dong Hu. So she decided to try and practice using her space magic while occasionally making some pills and potions for Ji Tian.
Base on Fang Yu's memory, she had tried to access a different dimension before, but she failed to keep the portal open. Moreover, she was afraid to go inside as she was scared that she stumbled upon a different world. However, this Fang Yu was different. First and foremost, she was following the original plot. Fang Yu found a way to go to the Ghost dimension and make the pill for Ji Tian.