Mother rat being aggressive

Question
My rat, Salena (I have asked you questions about her before), has been a great mother so far. She lets us hold the kits no problem and is taking great care of them. However, I recently brought home a new rat, Minca (I'm guessing she's around 2 months old?), from the petstore. She is a real sweetheart, not aggressive at all. When we first introduced her to Salena, they got along great. But when Salenas babies (4 weeks old) went in the cage near Minca Salena suddenly became very agitated. Minca was being nice to the kits. She was very interested in them but not acting aggressive. Anyway, Salena's fur got all puffed up and she started shoving Minca around. I looked it up and i think its called sidling. She was rubbing against Minca, shoving her head under her, crawling under her, acting really strange. They broke out in a little fight (not serious, no injuries) so I had to separate them.
After that Salena started getting aggressive with her other cagemate, Denali, who she has always been fine with. Denali is about 2 and Salena's lived with her all her life. They didn't fight but she was doing that same pushing thing. Denali just ran away. Then, later, when Minca was crawling around Salena's cage, Salena was lunging at her through the bars all puffed up. But she's still fine with us. Why is she doing this? When will her maternal aggression go away? The babies should be weaned about now but she's still nursing them regularly. Is this normal?

Answer
At 5 weeks you need to call it quits and separate babies from Mama. At that point, they're done, and she needs to know that as well! What Salena is doing is entirely natural and that aggression won't fade until her babies are weaned and her hormones quit surging. Keep the other girls away from her for their safety and reintroduce them a week after weaning and you should be A-ok. Good luck!