Vanessa's case was much more complicated than Sylvia's. Sylvia cultivated her power from scratch carefully and meticulously, supervised by the Devil Emperor. Apart from other help, Sylvia spent five years in Quadtria purely to strengthen herself and was already broken through to half-godhood before her true divine ascension.
As for Vanessa, she received the power transfer and legacy from her late father, the Beast Emperor. Even though she had already fortified her foundation during the last five years, her spiritual root was actually still one rank below her true cultivation power.
Not to mention, the spiritual sea in her dantian had yet to become one grand unity, still separated by multiple pools. She was also still at the mid-stage, two minor realms beneath Sylvia before the private assistance.
Regardless, as long as one had reached 10th Rank, it wouldn't be impossible for Elysia to tweak the trick to help her people achieve godhood.
If the plan doesn't work nor fit, change the plan, not the goal.