She was 15 when she left the UK. She was born in this country and is a British citizen. Although she is of Bangladeshi heritage, she has never lived in Bangladesh and would have now means of support. Anyway, it appears that Bangladesh, quite understandably, does not wish to take her in.
Some say she is truly wicked and manipulative and deserves to be stripped of her citizenship and doomed to be an outcast in the world. Others think she was a naive and impressionable girl who may well not have understood the true nature of the regime to which she was fleeing.
I subscribe to the latter point of view and believe she may still be still naive, and emotionally and intellectually immature. Anyone who was truly crafty and manipulative would have appeared on TV weeping and wailing and saying what a terrible crime she had committed, how much she had come to realise that she loved Britain, etc, etc. Instead, she came across in a fairly blank way - and emotional detachment can be an indicator of trauma. She neither apologised for her actions nor displayed the sort of emotions that may have invited sympathy.
Whatever you think, as others have said, why on earth should another country be expected to take her in, and presumably support her?