The writing style of a quoted source within your paper would not be a reason to revise the paragraph wherein the quote is contained. Every writer has a certain style, and it could be said to be unique, subjective or personal. As long as the passage quoted is well referenced and well transcribed, and as long as it follows the argumentative coherence and congruity, its style is not a matter of concern to whoever chooses to quote it.
If i am to use a proper spelling and grammar, that sentence could be changed into : The store, with its half roof covered in snow, was freezing to the point where the customers were visibly shaking
"She" is the only third person singular pronoun used in all 4 sentences. "Will have been" is the future perfect tense and these two combined make the third person singular, future perfect tense.
