Time is what it takes....great that she is settling in well.
I helped raise 5 kittens at my daughters’..with existing adults..My Silky was the “surrogate mom”..so I had hopes!
I have seen her groom both kittens yesterday without it ending in a hiss.
She and Smokey both have to get away at times from the younger one ,Rocky Balboa, who leaps on..and wants to fight Smokey just when she is relaxing with me..
I have kitten rivalry and queen of the house syndrome to deal with..LOL