State boarding, or similar/language immersion/mildly alternative?

Why can your db and sil not find another, less rigid, school where they live in Europe instead of all this effort in the UK? They are the parents after all! I actually feel sorry for this child. Does your do and sil need to be abroad? The only suitable solution here would be a cheap day school, that they can afford, or state school near the grandparents. A final decision on where the child is living and who might pay needs to be resolved. Do your parents really want all this responsibility that will curtail their life? Seems like a lot to take on when it is not their responsibility.

mummytime your right I've just read that. An interesting school with a positively glowing ofstead report. I wonder why the OP's dad thinks it's a good place to send his DD? I would have thought a bit like a Steiner school to be really happy there you've got to be 101% signed up to its ethos and beliefs. If you are then all other schools are just not going to really do it for you. I also suspect the school wants people who are going to stick with it, from reading their website I doubt they're looking for people who want to do it for a couple of terms then return to main stream ed.
OP you mention that she's vulnerable to be being bullied and that you think a structured school might help, I'm not quite sure if I understand that (maybe I'm being a bit daft). It's all about ethos of the school and how quickly and in what way they respond to bullying, not really IMO about structure. All schools day or boarding state or independent will have the odd bit of boarding. But you do have to remember that at boarding schools there's always going to be a bit of what many will call "banter" some children shrug it off and it doesn't bother them, others are upset and for them its bullying. Secondly in my now extensive experience of boarding even within a school there will be differences, especially between houses, where different house masters create different atmospheres and also a lot depends on you fellow house mates. It only takes 1 unpleasant individual to create a difficult and unpleasant environment for others good schools bviously address this but you can't change things over night. It's also inevitable that house staff can't supervise 60+ children's every waking moment. Fairly obviously unlike a day school children are there 24/7 so for a very sensitive vulnerable to bullying child this could be very difficult.

If it the same one, on reading their website I think they only accept students starting up to 11, but do keep them until older.

"Well I thought the school it was seems to go only to 11 these days"
mummytime the only boarding school I know who have optional lessons state on their website that they go to 17.
I'm a great advocate of boarding but in my personal opinion a slightly nervous reluctant learner would probably struggle. Boarding school children have to be quite robust and are expected to shift for themselves in terms of their personal lives but also their school work they obviously aren't supervised to the same extent as a child at home could be.
On the other hand most boarding schools do have lots of routines (although this may not be the case with the school her parents are thinking about which I know nothing about I must add).
What does she feel about boarding? Does she make friends easily?
Boarding fees are very expensive most are at least 30k+ PA many will be significantly more than this and fees rise year on year if she's yr 7 that's a pretty he pity commitment.

Well I would find the most senior person in education that I knew and ask their advice, any good Head Teacher would have valuable things to say, I would ask if there is a SEN co-ordinator who may assesses children privately for SEN? Maybe there is such a thing. I would ask ask ask advice. I would think about a psychotherapeutic approach too. There is a child psychotherapy centre in London, they may well have contacts all over the place. I would want to keep this child close to her family, slow everything down and take as much neutral advice as can be accessed. I was a child that could have done with that kind of broad thinking and advice taking. Families are often very biased about what to do with kids for a thousand reasons, often subconscious and deeply painful. Sometimes a child triggers a painful part of a parents past and the parent can reject the child without knowing why.
this centre here may be able to put you in touch with a practitioner in this country or abroad.
Best of luck

I would second having a look at Quaker schools - Bootham, the Mount and Ackworth in Yorkshire, Sidcot maybe not too far from your DM.

'Mildly alternative' probably describes them nicely - and a very caring ethos, huge emphasis on pastoral care and nurturing the individual child, but the structure it sounds like your DN needs.

I am hugely, in theory, in favour of the approach in the school your DB favours, but DS is also an anxious and tricky child with complicated SNs and I don't think it would suit him in any way at all.

To put a sensitive child into a school with uncertain funding would be extraordinary and manipulative and putting her at risk of unnecessary change.

strange

I think the child needs better quality assessment and in my experience of two boarding schools growing up, she needs to be at home if at all possible.

I think everyone here is involved in too complex a way.

I think ideally the parents would say to the parents to find a way to love and care for their own child within their own budget.

This will create clarity of responsibility and the avoidance of shifting parental responsibility back a generation. Not uncommon, but not always good for the child.

This child's needs sound unclear.

Just my opinion!

Nervous, possible SN and parents overseas?!
It would be completely negligent to send such a child to boarding school. If the education system in her home country is such a poor fit for them the only option is even consider is 'naive gentle day school' staying with relatives.

Well the school I thought it was seems to only go to 11 nowadays, so it can't be that one. (It did used to go to 17/18).

Quaker schools have good reputation for a nuturing environment. Some are boarding.
www.aquakereducation.co.uk/

I only know of one boarding school where classes are optional and it's very cheap. £12K a year I think.

It could be a perfect school for her.

A state boarding school cannot offer what this alternative school does.

Keswick is also State Boarding - much smaller than Dallam. I don't even know if it takes children that aren't 'local' (as in Lake District kids that couldn't get to school in a reasonable time). There are a lots of small schools in Cumbria too. Settlebeck, Samuel Kings, Kirkby Stephen Grammar (not a grammar), Appleby Grammar (likewise), John Ruskin etc. Although I know this doesn't solve your space dilemma.