she must know

She opened a drawer and took out a piece of red paper as I sat in the shadow of the curtains in the already dim room. She must know I was watching but continued to write the secret message.
Is the above natural and correct?
Thanks.

That's what I thought. Could you check and see why the author uses the present tense?

She had the most exquisite rear end, round, white and soft with the foxiest curves you were ever likely to see. She must know I was watching, but she continued to pack up her stuff without giving any sign that she was embarrassed or worried in the least.

Thanks, Optilang. Maybe another native speaker will confirm this.

By the way, is it also correct to say "the author uses" instead of "the author has used"?