I’ve got no experience of the places I linked to. I have done a fair bit of fly fishing though (marriage, kids and other interests mean less often than a few years ago though).
I would agree with the comments above that a stillwater is the place to start. Generally on still waters you have much more space to cast.
Once you’ve been taught the basic cast, you can practice on any open grassy place using some sheeps wool or something instead of a fly.
She will also need to make sure that she gets a rod license from the post office once she gets started (but shouldn’t need one when with an instructor with a coaching license).
Hawkshead fishery on Esthwaite in the Lakes are running some free 4 hour beginners tuition days on a few dates this year (well free apart from a £10 admin fee). It’s a stunning location which I’ve fished a few times before. There’s great access to the Grizedale bridleway network from literally just above the fishery so happy days.
http://www.hawksheadtrout.com/school.html
http://www.streetmap.co.uk/map.srf?X=335952&Y=495525&A=Y&Z=115 – the byway into Grizedale with the green dots is good fun in both directions.