Oh dear I don't think I can help with this one I am afraid
However.................................why not try a bit of sibling education.
Rather than Gloucs/Worcs/Hereford/Wilts think next stop Iceland.
Indoor facilities when raining............a campers kitchen.
Shopping.......................there is a Spar next door.
Good facilities................there are 2 toilet blocks.
The ideal place
http://www.sangosands.com
You never know, it may be the start of a Bongo adventure for her, all it takes is some gentle persuasion and she will realise that camping for exceeds the pleasures of glamping.
Seriously though, I hope you both have a great time.

Why?...........Because somebody might wave back.