Thank you for your email. I understand how worried you are about you niece.
As moms and aunts we instinctively want to feed our offspring, and with all the love and good intentions that go with feeding them, we sometimes become 'obsessed' with what our children are eating and how much they are eating, watching over them like a hawk. This well meaning instinctive behaviour however, can cause a lot of anxiety and stress for our children resulting in eating disorders later in life.
I sense that your niece is rebelling to the pressure she is feeling at "being forced to eat." None of us can eat when someone is standing over us telling us to eat. The stress she is feeling literally will make her unable to chew and swallow her food. When we are stressed we grit our teeth, feel a lump in our throat, butterflies in our tummy, and develop a dry mouth making it hard to eat anything. As she is unable to tell you all to please leave her alone, she is doing the only thing she can under duress and that is not eat.
It is also important to establish if she has been bullied at school about her appearances and if this is in anyway contributing to her not eating. If you can allow her to talk about her concerns without passing judgement you may discover the underlying cause to her not eating.
In the meantime, I would suggest that adults around her apologise to her for putting her under so much pressure and "forcing her to sit at the table for an hour or two while she finishes a meal".Explain to her that from now on things will be different and she can decide when she wants to eat and what she would like to eat.Tell her she will be able to serve herself dinner, lunch etc from the family meal if she wants to but that she will also have her own snack draw filled with dry fruit, nuts, biltong, crackers, whole-wheat biscuits, energy bars, raisins that she can help herself to when she is hungry. Give her permission to help herself from the fresh fruit available around the house and the fridge which should be filled with yoghurt, yoghurt drinks and smoothies. custard and vegetable sticks to snack on, and also tell her she can eat anywhere she likes even if it is in front of the TV.
She may be a bit hesitant initially to take charge of nourishing herself, but do encourage her by giving her permission and then leaving her alone. I would recommend the family stops talking about food and eating, and do not comment on what she's eating or not eating, how she eats or how much.
It is important to give up the control of her eating which may not be easy for you and her mom to do especially if your family life and cultures are centred around meals, and I would recommend you seek counselling to help you do this. For now your main concern is to get her eating again and she can only do this if she feels relaxed and in control. Once she settles and begins enjoying her food again, you can ask her to join the table and follow a routine, For now though she needs to be in charge of her eating..
She will instinctively seek out food when she is hungry, and you can supplement her diet with vitamins and omega 3 fish oils. If you find that after several weeks of following my advice her eating habits do not change then take her to your paediatrician for a general check up and a child psychologist for play therapy.
Good luck and let me know how you all are doing.