It is possible to get a place in-year, but it depends of course on places being available. As you're looking at Y7 and she took, and passed, the tests, this should make it easier in that the schools would be unlikely to ask them to take a fresh test. Were it Y8 or above they would probably ask them to sit new tests (maybe English, Maths, science) and then compare the results with the current Y8's.
Passing the test is all well and good, but if the school is full, you might have to appeal. Several of the schools are now 'topping up' - which means they will take children from the top of their waiting list (which in itself fluctuates) to top up over the Published Admissions Number to the maximum they can fit in the year - while PAN for a school may be set at 112, they might be able to fit in 120. This is after appeals have taken place for Y7, and at any time that a space becomes available for Y8 up.
My question is, if the move to Gloucs goes ahead, does anyone know how likely it is that she would be able to transfer to a GS in Gloucestershire, possibly in the middle of Y7? We would be most interested in SHS or HSFG. Would the best idea be to appeal or to go on a waiting list? Or is it impossible to transfer in year and she would have to go wherever there is space?
Go on waiting list and appeal as well. Neither has any effect on the other, so you can get a place off the top of the list even if you loose an appeal.
Your problem is that you may have to send your daughter to another school while waiting for a space to come up.
Speak to the Admissions Clerks at either school, just for an 'in principal' chat - they do tend to be helpful - don't treat them as the enemy but as a friend.