Thanks for all your advice.

An update on our situation.

We went to the solicitor and they pretty much gave us the advice that you guys provided, plus the requirements for obtaining a visa in the future (income etc). This was free as she had seen them before.

So now she will obviously go back home with the minimum of fuss, hopefully, and then we can take it from there.

Solicitor did say to not admit that we had met here previously, as in ignore all knowledge she had been here, she will get new passport once home. Then stage an online meeting and related conversations prior to her going, and maybe I visit on my own and make it look as though we have met in person, prior to actually having any visits together etc.