The Frome <> Paddington train tickets could be over a hundred pounds for return tickets, I don't know if she'd qualify for a concession since she's on disability. Then the Hilton for two nights, if I've searched right that averages at £140 per night for an adult & child.
Just the afternoon tea (2x £15), theme park (2 x £29), ghost bus (£25 adult, £17 child) would be £130. Doesn't count the dinner or any other incidentals, even sticking to a budget it could easily be a £500 trip.
Didn't take long to find all of those prices, I am only mildly curious. It is possible family helped, or she has got discounts on some of these things. I don't really begrudge her son getting to experience a holiday, it just isn't the lifestyle most people on benefits get to have. If a person off work sick you'd think they wouldn't be able to handle such packed days.