The conditioning within the org is deep so part of it is a throw back to the old values and way of life but looking at the situation from the outside it would appear that you are beating yourself up needlessly.
firstly your girlfriend is 38 well able to make her own decisions and hold independent views.
Secondly she has entered into a relationship which she knows does not meet the criteria for a witness and furthermore has become intimate with this person fully aware of the consequences. You did not encourage her to start or maintain this relationship and you reminded her of the likely consequences.
Thirdly she already has her own doubts about the organisation and has done her own research so knows that some of what she has been taught is man made.
In my opinion she is already half way out it is really only a matter of time. At 38 she has found what she may feel is love my only concern would be whether the man in her life sees her as a bit of fun or something more permanent. If she is lucky he will want to be part of her life and spend his life with her if she is unlucky he could ditch her when the going gets tough leaving her in need of a friend.
People make their own choices love, infatuation and hormones are more powerful than housesitting for you. You have told her no lies and left it to her to make her own decisions don't beat yourself up about it you really don't have anything to be guilty about except not lending her CoC to read.