Do remember that I can only give you my opinion.
Another lawyer may have a different opinion. Litigation needs at least 2 parties and neither goes to court expecting to lose.
Nonetheless, one of them does, even though they have been told by their respective legal advisers that they have a good chance of success.
If there was a black-and-white answer to every legal problem there would be no need for anything to ever proceed to court.
In my opinion if you were to stop her trading, she suffers loss.
You would only be responsible in respect of complaints from customers if you were trading as a partnership, not if she was on her own. If there was evidence that you were not trading with her, but in my opinion that absolves you of liability.
You have not mentioned before that you had to pay GBP3000 per year to lease the land from her when you were running a business.
“Partner”. Semantics. You are partners in the land although you haven’t mentioned before that the campsite was your business for which you paid GBP3000 to lease the land.
If you have a lease of the land then this you are free to close the business and open it as you wish provided you continue to pay the rental.
If you want to sell the land, and she doesn’t, and she won’t, then you can apply to court for an order for sale under section 14 of the Trusts of Land Appointment of Trustees Act to compel her to sell AND you can ask the court to award costs against her. It is unlikely that she would be able to successfully defend any such application.
It was not apparent from your initial question that this was you’re business and that she was in effect just a joint landlord with you. However with your further clarification, then she is not entitled to run you’re business any more than she would be entitled to run a chip shop which was you’re business albeit that you were jointly the landlords. A landlord cannot simply step in and run someone else’s business purely because that person has decided they don’t want to open the shop any more so to speak.
However notwithstanding the business closure, I assume that you have still be paying the GBP3000 per year lease otherwise on are probably drafted lease, once the rent is 14 days late, then the landlord can foreclose on the lease and it ends.
She would be entitled to do that on her own because notice by one is notice by both. If that’s the case, then your business ends but provided the rent is paid up to date and has never been late, then she has no right to run your business.