strange queen behavior

Question
I have a 3 year old calico Hemingway cat that has just had her first litter of 3 kittens. They are now 2 weeks old. She also readily adopted an abandoned kitten that is 5 days younger than her own, and until now has taken great care of them all equally. (For background info, let me note that she has had no objections to me handling the kittens since birth, in fact when she enters her nest, she often lays on them and will roll onto her back and cry at me until I put them up to her belly to nurse.) Today however she removed the adopted kitten and left it in the floor but cried for it when I picked it up. I put it back in the nest and she has since fed and cleaned it without incident. I also noticed, though, that she was biting the top of the tail area (her kittens are bob tailed) on one of her own kittens, causing it to cry out.I inspected for fleas, dirt, etc and found nothing. Should I monitor her for aggressive behavior toward the kittens or is this acceptable behavior? Could she be low on milk and trying to remove the weakest? Her behavior toward other animals has always been unpredictable and sometimes aggressive, even though she hasn't shown aggression to her kittens before. Any info you can offer is greatly appreciated!

Answer
Is it possible the kitten fell out of the nest??  If she is cleaning and nursing it she is not abandoning it.   I would just keep an eye out to see that all is well.  The biting is just aggressive cleaning.....and I don't worry unless there are puncture wounds.....kittens always cry or fuss when being cleaned.
If you are worried about her milk...buy some marshmallow capsules at the health food store.  Either give one to mom or open it and mix in her food.....twice a day.  That stimulates milk production.  She should be eating canned food and even kitten food canned with some water added to it to make sure she has the needed fluids for milk production.

Hope all goes well