Hi Exam Mama,
I am not familiar with St Helen's School for two reasons - I only have boys and I'm in a wrong part of the country, but out of curiosity, I went to their website and watched their videos. I was so impressed! Not just because the school and the grounds look lovely, but mainly because every single girl in those videos is happy and relaxed, whether in a science lesson, playing sports or in a ballet class - and how many schools have ballet classes for their pupils?
One of the girls in the second video talked about their induction course, how enjoyable it was and how it made it very easy for her to make new friends and settle into the school very quickly. Would it help if your daughter watched those videos again? Do you know when the induction activities are due to take place? If it's going to be a while yet, maybe they would agree to you and your daughter having another tour of the school, so that she can put her mind at rest? I'm sure they would be fine with that.
I understand your daughter feels upset that she didn't get into the school she wanted, and perhaps worried that she will not know anyone in her new school, but there will be loads of other girls in the same situation and they will all want to make new friends. Also, going to a different school does not mean that she has to lose contact with her current friends - weekends will be there to catch up and share experiences.
St. Helen's looks fabulous, I wish I went to a school like that!