Annie, all my instincts are saying that you should make the move and I'm convinced that, in your shoes, I would do so. However, I acknowledge that I am not in your shoes so I can't see the situation through your eyes (Sorry. Too many physiological metaphors here).
Your younger daughter is clearly a lovely, caring person and this would give you such a great opportunity to bond and be friends as well as mother/daughter. Perhaps, with her close by, you may even find the courage to venture out again and explore your new world. But, one day at a time ...
Lincolnshire is a beautiful county. You haven't said which part of it you're looking at and, while the southern, fenland area around Spalding, Holbeach, Boston is very flat, it has it's own charms. Further north, we have miles of lovely, rolling countryside and beautiful towns - Stamford, Louth, Alford are a delight and there are dozens of pretty villages hidden away. I admit that, as a Yellerbelly, I'm prejudiced. I had 40+ very happy years in Essex but returning to Lincolnshire was one of the best things we've ever done. Even my dyed-in-the-wool Essex Man OH agrees.
Only you can decide but, as someone else has said, the grandchildren have grown; you kept your promise to your elder daughter and have nothing to reproach yourself with. Time to look after YOU, now. We only get one go-round so carpe diem. (((Hugs))) to you.
PS. Just an afterthought. We got a highly strung, ageing and easily spookable cat up the motorway from Essex in the back of an overstuffed car with negligible ill-effects. She's always been a fairly hysterical traveller but with careful planning and preparation, we kept her calm and didn't need to resort to the vet's offer of tranquilizers. I'm not suggesting you need a vet(!) but I'm certain your journey from Wales could be planned and managed to minimise distress when the time comes.