I know nothing specific about the school, but you can find out a lot by picking through all the documents in the admissions section of the website.
On thing: it says all applicants must fill in and return the Supplementary Information Form and that the deadline for this is 20th October!! The form is available on the website and it needs a passport type photo.
Also, I can't work out whether pupils with language places need to attend the assessment / banding tests in December. The school will tell you.
Were there no instructions in the letter telling you what you need to do next?
You will need to put this school as your first preference on the CAF if you want to take up the place, because under the equal preference system if you put another school as first choice and that school has a place for your dd the LA will allocate that place to you and turn down the Greycoat place on your behalf.
If however there is another school that you actually prefer I guess you can put that first and if that school cannot offer your dd a place she will get offered Greycoat if that is your second choice.
That is how I understand it, anyway.
If you liked what you saw on the Open day, a single sex school will suit your dd, the journey is OK, and you are happy with the CoE nature of the school (attendance at Abbey etc) then what's not to like? She has obviously done extremely well!