https://www.quest88.com/ comes up on the ICE dealer list. Looks like they've got some Hase stuff too. (Trikes are probably a good starting point, as you don't have to learn to balance them.) Otherwise you're going to be travelling much further afield (London, Ely, Edinburgh, that sort of thing), as recumbent dealers are somewhat rare. If it comes to that, you could do a lot worse than a visit to D-Tek.
What's her issue with DFs? Arms? Balance? Back problems? Saddles? That'll have some bearing on what might be suitable.
The York and Mildenhall rallies are good places to spot recumbents in the wild, chat with their owners and maybe have a go, but it's the wrong time of year for that. BHPC meets similarly, though they tend to be more at the ludicrous racing machines end of the spectrum. I dare say we could arrange for some of YACF's resident darksiders to congregate for a pootle if it came to it...