Ms McCann last year placed a total stake of almost £25,000 on the horses, and would have come out £985,000 richer had bet365 not refused the payout.
The bets stood across 12 different horses, in four somewhat obscure races.
Bet365 refused to pay out on the basis that they believed the stake was funded by 'a third party'.
According to bet365's lawyers, if prove, this would be a case of fraud, however Ms McCann has stated there was no wrong-doing.
Ms McCann has sued for damages totalling to £1,009,960 (€1.1M).
According to The Telegraph, Ms McCann contacted bet 365 a day after her 'win' to withdraw her funds, and had this much confirmed by a 'live chat' agent.
The next day she got a call from the company, where they asked her a string of questions to confirm her identity.
At the end of this call, apparently satisfied, the agent told her her request would be processed within 48 hours.
The money never came. Instead, her account was suspended, and she has not seen her original stake returned either.
Apparently, bet365 have a 'no third party rule' in their terms and conditions.
Ms McCann's lawyers have disputed however, that these are “too lengthy, too complex and much too vague for the average customer to understand.”
They also suggest that these rules could prevent syndicates from betting, and could mean “the husband who puts a bet on the winner of X-factor for his wife, or on the winner of the Grand National, would have those winnings ‘robbed’ of him.”
In a letter sent from Ms McCann's lawyers to bet365, they say “Our client’s case is very straightforward. She placed a bet with your client. She won. She is entitled to her winnings.”
Bet 365 responded by saying “Our client has reasonable grounds to suspect your client to be guilty of criminal offenses including fraud by false representation; cheating or attempted cheating.”