We found as returning expats that Orleans also had zero interest /experience in handling pupils who were moving from another country, or perhaps I should say ones who were not doing so with very apparent language or other cultural adjustments to make which would clearly affect their performance at school. Frankly the same applies to eg any pupil with moderate learning difficulties who still attains above the average level. There simply aren't the resources to focus on the individual needs of pupils if they are doing "OK" , or maybe it is a cultural thing...... However we were met with blank and disinterested faces when we mentioned DD was returning from another culture. I don't think that you will be able to argue that Orleans is going to be distinctively different enough in its approach to make a winning point at appeal.
I am surprised there were not places at Orleans, I have known quite a few local pupils move in there out of year. I am also surprised given all I have heard of RPA that your DD is being ignored quite as much as she claims. They have smaller classes for a start, and are working really hard to improve their reputation. Remember that every class in Orleans will be full and they face the same issues of crowd control (even at Waldegrave, I have friends who teach there) .
I really sympathise about the journey and the fact that the school does not serve this community but I do not think that her actual school experience at Orleans will be that different.
There is a big contrast to the independent sector where it was made very clear that DDs experiences would be valued and that they understood the difficulties faced when teenagers are facing fitting in to a new culture. I am not so sure St Catherine's is a rock solid nurturing option though. It is a lovely school but I have known difficult DDs be sent there to get away from a bad crowd and bringing their bad crowd ways with them, no school is immune. However I am assuming private is not an option. If it is there are a lot of good independent schools around and many local DCs go to them, often because they cannot get into the good local state schools. Plenty of local advice available.
Don't underestimate the difficulty for a teenager fitting into a new teen culture, even if on the face of it they are not dissimilar. It is the most difficult time psychologically to cope with a move. Fitting in with peers is so important and it is every subtle detail that takes on a huge importance, the language, the music, etc etc. thankfully from Year 10 they start to appreciate that difference is good too. When DD was 14 we had a chance to return to the country we had all missed terribly, and DD was still very much in touch with her closest friends there but she was adamant that she did not want to go through the period of adjustment again. The teen culture of her old friends was perceived by her to be so different to the new one she was now part of (though on the face of it very similar). DHs company engaged Councillors to help you adjust to a move and they were very clear that the greatest psychological challenge was faced by teenagers.
One thing your DD may be finding hard to adjust to is that Brits, including teachers, tend not to be so "out there" as Americans and that can come over as disinterest. I have American expat friends with DCs at schools in this country who constantly struggle to distinguish between discretion and understatement and genuine disinterest \incompetence. I would certainly go into school (possibly in secret, I do understand the teenage sensitivities) and see the Head of Year to make sure they understand how your daughter is feeling. You may wish to try and avoid the " pushy American mom" stereotype that a few of my American friends feel is a problem....