My daughter did the exam last year and told me that they only said it was near ending with 30 seconds to go - I would certainly advise a watch to be placed on her desk.
One thing we did that my daughter said was helpful was to leave her Brothers at my parents house the night before so on the morning of the exam she had no brothers moaning, groaning or arguing in the house. Everything was peaceful and relaxed, no T.V just some of her favourite music playing at home and in the car - We tried very hard to stay as relaxed a spossible on the day and she said it really helped her.
Best of luck, I know it is a tough time!
My daughter came out of the exam and said 'it was quite easy dad' which was worrying, but she did pass and starts 5th september!