Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
In a word, no! It is a principle of UK taxation that one must live somewhere and usually pay for it unless one is very lucky. There is no way that the costs of her London room can be offset against her rental income for her Scottish residence.
I am so sorry to have to rain on your parade..
Thank you for your excellent support.