I understand the point you are trying to make, and the carer is clearly not doing his/her job. Maybe the best thing to do under the circumstances is to ensure the carer sits next to the lady and when she needs something point it out to this person. i.e. "Miss X is asking for her drink, could you help her, please?" The carer will get the message soon enough. If that is not enough, take carer aside (I would) and point out her job in simple English, out of the lady's earshot.
I feel sorry for the poor lady, she is clearly coming to the group because she wants to learn to knit. It is not her fault she cant knit at all. Also, as others have said, it is a way of having some social activity. She may lead a very lonely life.