I am sorry, I wasn’t around yesterday so only just seen this.
Firstly, if there is no domestic violence, legal aid will not be available.
However, it seems to me that there is domestic abuse. I would suggest that she contact one of the DA helplines.
http://www.ncdv.org.uk/ They may be able to assist with an occupation order or a non molestation order. That’s the first thing.
Second thing is the Declaration of Trust. This normally sets out the ownership of property. And yes, they are legally binding as long as the correct formalities have been followed. I am sorry to say that if she signed it the chances of it being set aside are almost nil.
// I've pointed out that his very unreasonable behaviour in importing his inamorata would invalidate any agreement and that advice received holds that it is not binding as it was signed under duress. She quibbled a bit about that, but I pointed out that he stipulated it as a condition of buying the house and that was duress./ Whilst I fully sympathise with the situation, I think that it is fundamentally unlikely that it would invalidate the DoT. Setting a condition like this when buying a house does not amount to duress. Naturally I do not know the full terms of the DoT, but I do consider that having it set aside (particularly when she had legal advice) is probably unlikely (not impossible, I might add, but on the basis of what you have said, unlikely).
I would suggest that IF she can afford it, she instructs a barrister on a direct access basis. That way she will only end up paying one fee and they will only do as much (or as little) as she can afford.