Sorry you won, perhaps, if you can realise the odds are stacked against you then and treat it as a great early Christmas present and not bet again then you can walk away a winner.
I was lucky, when I was just 18 I bet on the Grand National, I had an each way bet and my horse came in 2nd, I got my stake back £20 and £5 winnings, a lot of money back then, when I realised what I had risked just to win a fiver I realised it was a mugs game and the only gambling I have done since is occasionally on the lottery.  I have done many stupid things and still do once in a while but gambling is not one of them.  
      I remember losing a lot of money in a arcade, probably getting on for 20 or 30 pennies, a while ago. My mothers quote at the time stuck with me 'the only way to make a small fortune gambling is to lose a large one'. 
Had you thought of taking about £450 out of the account then let your daughter carry on and hopefully she will lose the other £50?