Maya Lahan is such a simple characterization, that a lot of depths one would expect is just completely missing.
For example, she is blaming Lucas / John for the death of Vaughan. But she is as much responsible as Lucas / John for killing him. Her not even realizing that, makes her seem very naïve and simple minded, which is quite unbelievable for a doctor. Her failure to render assistance for a normal person would be a bad thing to do, for a doctor it is just unforgivable.
Compared to killing Vaughan, having scruples concerning Ruth, a person of Lucas / Johns acquaintance she knows nothing about except what a stranger told her, seems quite far fetched. It seems like an attempt in vain to make a good person out of her compared to the through and through bad Lucas / John.
Her love for John cannot have been strong or have surpassed the long separation. She betrays John / Lucas at the first possible moment because of an explanation she got from a foreigner. She does not show the slightest scruples of betraying him to his enemies, but hurts him further by openly calling him an irrevocable murderer.
But here now her reaction becomes completely unbelievable. Why not ask John about his past life? When she now declares that she always has felt something was wrong with John / Lucas. His minimal explanation, that he has been in prison for a year completely suffice for her, as if that was something to recommend him to her now. Or do I misjudge her and she was in with the illegal dealings of John 15 years back?
She hardly speaks with him except emotionally blackmailing him into a future together. Also not a factor to really endear her character to me as a viewer or make her at least believably female ;o)
Perhaps her motivation was like Sarah Caulfield's from Series 8: “We had better things to do …” (Here I must state, a very male point of view. Are no females among the script writers?)
P.S.: You will have recognized the distinction in the title “Maya, the love of John’s life”. I am not of the opinion, Lucas North loved her. Otherwise he would have found a way. Is there not a saying ‘Love always finds a way’?