Some thoughts to take into account:
Don't forget to check out the differences in curriculum between the two schools.
For example, at BHS, the girls can choose to do 2 of French, German, Spanish or Latin in year 7, or if they want to do 2 modern languages plus Latin, they can do Latin as an extra subject at lunch time. These choices might be significant if your daughter might be a linguist. If she's a scientist, then perhaps DGHS offers 3 separate sciences at GCSE. (At present, to the best of my knowledge, BHS only offers double science). If she's into history and geography, can she take both subjects at GCSE?
BHS are condensing KS3 into 2 years, with the intention of giving the girls more flexibility with additional GCSE options or early start to A levels. Is DGHS doing the same?
How much time do they get for lunch? This could be important if your daughter wants to do lots of lunchtime activities.
What are the sporting facilities and clubs if you have a sporty girl? What about swimming?
What time will your daughter get home from school in the evening? What time will she have to leave home in the morning?
What are the homework policies? BHS has had a deliberate policy of reducing homework for year 7's. This year, there's a maximum of 3 subjects a night, to a maximum of 1hour 10 mins in total. In reality, my new year 7 rarely gets 3 subjects a night. This leaves her time for the multitude of other activities she takes part in. She even has time to play....!
Hope some of this helps