Almost all of our mamas have started laying again around 6 weeks and pushing the babies away at about the same time.  And I've also noticed the smaller the breed the sooner they "wean" the babies and the sooner they start laying again.  However, we have had a few die-hards!  One raised 5 babies, never pushed them away, and when they started leaving her some she would call them constantly!  And even when she would go to the nesting boxes to lay an egg, she would call them to her in there also!  But, that is rare!  Leave the babies with her, they'll have great chicken instinct!