"But in the present, she wrote me a long explanatory text that just does not jibe with what she wrote in the past."

Why did she do this? Is she going into this much depth because you demanded it? A Youtube video I saw said liars tend to explain things away with more details but perhaps you are intensively interrogating her--that might cause that reaction too.

// i sent her an exmail explaining how i read her on-train writing and that i needed to think about it, because I didn't know what to think of it. there were complications involved but that the gist of it. so, i asked her questions, which may have felt she was being interrogated

Her explanation seems weird but perhaps she is trying to tell you what she thinks would satisfy you?

// Yes, I think that's the case. She wants to save our relationship and will say whatever she thinks will work.

It is such a bad lie that I can't tell if she is hiding something important. Either she is true to you now or not.

// I know. I have my doubts. We had a rocky patch a few weeks past, and I stormed out. She called her abusive x narcissist boyfriend for solace. I don't know what went on between them but I do know she broke her no-contact policy to get in touch with him.

// I don't know if she's hiding something important. I mean, like what?

// could you tell me what, in your estimation, makes it such a bad lie? i have my reasons. i'd like to hear yours.

That is the only question you need to figure out. To bad you looked. Not being judgemental but sometimes it's best not to know/share nor was it wise for her to go in depth in her explanation....