Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
Your sister is buying a house when she already owns one. She will have to pay the 3% Stamp Duty Land Tax (SDLT) surcharge on acquisition. If she sells her original house within three years she can apply to the Stamp Office for a refund of the surcharge.
I do hope that you have found my reply of assistance.
Whether she lived there or not is irrelevant. If she owned it and no other residence then it would be classed as her sole or main domestic residence.
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