I have thought she could well be an undercover cop. However, about the 'definitely/definately' thing, in the messages before Hastings took over the keyboard, that were presumably coming from the OCG boss / H, it was spelt definately. I think the fact Hastings then also spells it definately himself, is just another tempter to lure you into thinking Hastings could be H.
However, if you remember, the IT woman that set up the spoofing session said something along the lines of they've analyzed the past style of messages and set up some special software to make it look authentic as well as spoofing the IP address/sender's identity. I'll keep an eye on whether they revisit this point.
As for sending a coded message, you can only really transmit one bit of information in whether you spell it definitely or definitately. So I'm sceptical about that particular aspect to it, but it's a good observation.