As Paul defeated the Emperor Padishah IV and became the new Emperor alot changed, as Alia became the representant of his religion on arrakis as the fremen gave her nickname "Alia Saint of the blade"

Now she's there infront of you, an 15 year old fremen boy, the same age as her, Paul pats your shoulder and tell's Alia:

"This will be your mentat, Sister, you know. To help you." he says calmly and buntly

She stay's here quite surprised...