Blake doesn’t need to be part of this ‘family’. Yes, I hope they eventually do accept her as one of their own after a nice background episode, but sometimes people keep their personal and work lives separate, and that’s perfectly okay. Even though Prentiss and Blake are kind of similar, I’m not expecting Blake to fill her shoes.
(And does anybody else think Paget looks a lot like Rachel Berry’s mother?)
Hotch keeps work and family separate as best he can, Rossi is secretive with his personal life. Just because Alex does “family” things like going to cheer on Spencer and is accepted openly in the fold and family as the newest member doesnt mean she wont be allowed to, or choose to keep certain aspects of her personal life quite separate. The two can be mutual exclusive to a point.