The vast majority of track works and disruptions aren't even up on the National Rail website yet for Easter - and that's not to forget that there is almost inevitably strike action around every holiday period. If it's genuinely a thousand mile round trip (the OP's reason for not arranging a car), that's an absolutely guaranteed way to fall foul of multiple disruptions. And it would cost an absolute fortune/take hours to do so even if she miraculously lives right by a completely unaffected length of the UK rail network.
Walking five miles to a village pub (or further) is a lot different to be stuck on a bunch of vastly overcrowded (if running at all and they haven't cut the previous services, leading to there being no reservations and being left with the floor of the vestibule outside the toilet to sit on) trains for somewhere around ten hours.
Thinking about flying down? Travel to the airport could be screwed. Then there's travelling to the destination. Add in more strikes, huge crowds, weather disruption and the need to have suitable ID for a flight. Maybe they have passports - if they don't, as they don't drive, they can't do that.
It would be nice to think that being in your sixties guarantees perfect health, but even my apparently perfectly healthy right up until that moment siblings have started dropping like flies at exactly the age range concerned. There's also sight and hearing changes to take into account - walking in a lovely, quiet patch of greenery is completely different to navigating public transport on one of the busiest weekends all year when you can't quite see properly and can't hear what's going on.
In short, I can envisage many reasons why a journey of that length on that weekend is out of the question for people who aren't middleaged (ie, 35-55ish), they're knocking on 70.