Cats don't see their kittens as their "babies." They have extremely strong maternal instincts for the vital 6 weeks it takes to get them to the point they can eat mushy solids, and they have an instinctive urge to give them survival instruction up to an additional 3 or 4 weeks. But that's the limit as a rule, although I have known cats that stayed bonded with their kittens for up to a year. One of my cats did this, but she came to me with nursing kittens, and as soon as they could eat on their own, I had her spayed so she was no longer at risk of being bred. She "adopted" only one of her three kittens to take back to the wild with her, and I gave the other two away to good homes. But normally a female cat is ready to mate shortly after she decides that enough of being followed around by a bunch of kittens is enough, and then her kitten is in her way. The cat I had who stayed with one of her kittens wasn't conflicted by mating urges, and so there was an unnaturally prolonged interdependence. We humans are usually the cause of this shift in behavior by our interference -- keeping them in the same house together, spaying, etc.
What has happened is that your mother cat sees the kitten as a rival, not her baby. She is probably jealous and angry with you for forcing her to accept a rival in the household. Try to see things from her viewpoint, and see if there is something you can do to make her feel more secure in your attention. I personally would get them in the habit of being fed a few tablespoons of some tasty canned cat food once a day -- separate dishes and one at one side of the room and one at the other. Stand (or sit) between, and the cat that is finished first can be scooped up and put in a cat carrier box if it shows any inclination to start for the slower eater's dish. The separated cat can see through the wire or mesh of the box that the other cat is not getting extras. As soon as the other is finished, you can let the other out of the box. Talk to them with affection in your voice when you go through this maneuver, and don't shout or hit them even if they try to behave badly.
At first they will hiss and spit and even claw at you, so watch out. But they are not stupid, and they will understand that you will not tolerate stealing from each other's dishes. Never leave a dish on the floor with leftover canned food in it. It will cause fights, even among friends. Get them used to locating their own feeding dish (for dry food) at separate places in the house. One might be shut in the bathroom with hers for a few weeks at feeding time, while the mother might really appreciate being left a snack-dish on top of the refrigerator where she feels she can defend herself against her rival (the higher up she is, the more status she acquires in the catworld). Never hit them -- talk to them gently and steadily and with great patience as you would a human baby. Use the same tone of voice. It soothes.
Always be sure that you are giving both cats equal attention during the day. But deal with them separately. Don't try to force them to inhabit the same room or the same playtime.
Always talk to them. Tell them stories, sing soft songs (like lullabys or soft love songs -- not rock and roll or disco type stuff), give them both little pats throughout the day to let them know you care about how they are feeling. Don't linger with the mother cat if she is hostile. If she seems quiet, touch her head very gently (don't pet) and then remove your hand in a slow, steady motion and back off. If she thinks about how angry she is with you for forcing her to share her house with a rival, she will lash out. don't punish her if she does. Speak in a distressed voice "Now why did you do that? Now you've hurt me. Poor kitty, I'm sorry you are so upset..." and then go and wash your scratches with a good soap and water -- put pressure on deep scratches for a while until the bleeding stops. Bandaides for the ones that don't stop right away... Don't panic. Don't punish the cat. She is just deeply hurt by your insistance on her rival sharing everything. If you have endemic catscratch diseases, you can pour some peroxide into the wound (get it diluted for this purpose at a pharmacy -- it is cheap and effect). I have never gone further than an immediate wash with soap and water, and I have never had an infected scratch or bite from a cat.
If there is no improvement in your mother cat, let us hear about it. Among all of us, there must be an answer that will fit the personality of your mother cat.
Best of luck...