Liye didn't like too much the option of transforming Aiwai because there had been a mutual opposition between beasts and the other lifeforms in the universe and there weren't a lot of experts like Liye who didn't mind about it.
Liye had several divine beasts as disciples in other worlds, so he was well aware of the problems Aiwai would face if she chose to transform.
The reason was mainly that the only beasts that could think like the other species were divine beasts or beasts that had turned into Origin Beasts, which made the other species to think lowly of them.
Thus, he felt that if Aiwai chose to transform into a beast, that would pose problems for her in the future as she would be considered a beast.