It's possible that the cat who is biting the grooming brush may simply not enjoy the sensation of being groomed, and is expressing her discomfort by attempting to bite the brush. It's also possible that the cat is experiencing some discomfort or pain while being groomed, and is reacting to that discomfort by biting the brush.
It's unlikely that the behavior is related to territorial marking, as cats typically mark their territory through scent marking rather than biting objects. However, if your cat is exhibiting other territorial behaviors, such as spraying or aggressive behavior towards other animals, it's worth consulting with your veterinarian or a behavior specialist to rule out any underlying medical or behavioral issues.
In the meantime, you might try using a different type of grooming tool, such as a soft bristle brush or a rubber grooming mitt, to see if your cat is more comfortable with a different texture. Additionally, you could try offering treats or positive reinforcement during grooming sessions to help your cat associate the experience with something positive.
