I think that the best thing is to speak clearly whith the student but in a light way, often some humor about the cituation is the best thing for not to loose the student, is a good thing dont take all aspects of life to seriously or to estructurated, and learn to be more flexible not only in our fisical body, enjoy your students and act compacionate its a honor to have students and to traspass some joy conciense and freedom to them...
pd: sorry my english
Alternatively, simply tell her that her tardiness and demanding attitude in the class is disruptive to you and the students. Inform her politely and firmly if she cannot show up in time to focus and be present in her body by listening to you and her own body wisdom; well then she'd be better served going elsewhere.
In my 15 years of teaching, I've found it serves everyone, including me, far better, if I'm honest with students who do not and cannot osberve the integrity of the class.
She will no doubt be offended but will learn more from you in ten minutes than many hours of frustrated 'pussyfooting.'
One other thing to consider in these situations that ought to be mentioned, is to look wiithin. Remember that, as yoga teachers, our students are nothing but mirrors, and what we dislike in them is a refelction of a part of ourselves that is not yet brought into wholeness. As Sri Aurobindo said, "It is not that we must cease what we dislike, but that we must cease to dislike." By finding all the subtle places inside ourselves that are unaware, or disruptive, and by brining our awareness, consciousness, and love to those parts in us, we will cease to dislike that in others. Thank you.
I had this very problem with two students, both infant school teachers, who habitually arrived late, chatting to each other, making lots of noise even though they could see the other students were already quiet and settled in their practice. I did eventually talk gently to them. They stopped coming at the end of that term. Whilst I'm sorry to loose any student, I still feel I did the right thing for the sake of the overall class. I hope when they are older they will one day seek yoga again with a different mind set.