Hill thought it should be Rose... Her Spider Magic Net was originally modeled after the Shadow Weave, not to mention that she also took a piece of the Pseudo Magic Net when she left Gerns World.
For the other deities in Toril, Shaer cannot be easily offended, but for the Spider Queen who comes from another universe and now resides in the Bottomless Abyss, it doesn't matter.
Of course, Rose is afraid of Shaer... but that's because Shaer's power and the strength of her subordinates far exceed the Spider Queen's.
Therefore, the cunning Rose never openly opposes Shaer. Although Shaer is unlikely to rush to the Bottomless Abyss to eliminate her true form, she could easily wipe out all her followers in Toril.
Moreover, Shaer is even stricter in guarding the Weave than Mystra... for instance, Rose's original goal was to take away the entire net of Gerns.
William's ability to so quickly know how to collect and utilize the Weave certainly means he had a good teacher.
