Yep, she(he) was definitely trading. Ultimately though, they should pay because they increased her betting limits after she'd lost heavily. That's what is so poor about this case.
A couple of other things - if you want value on long prices, ALWAYS head to the exchanges. It's not uncommon to get 120 (less commission) at the exchange where a bookie might offer 33/1 or even 25/1! The bookies are more competitive with favourites though, and often come with good offers like moneyback if 2nd to the SP favourite, that sort of thing.
And Sunbets prices are indeed toilet for the horses, but their football prices are quite reasonable.