[susan53]

As I said. There is no such thing as future in the past as far as verbs are concerned. All English verbs which refer to time are either present or past. There are no future forms. Compare ;
1. Sorry I can't talk to you now. I'm having a meeting with John.
2. Sorry, I can't come tomorrow. I'm having a meeting with John.

The verbs are identical. Both express a present on-going event.

(1) is a present event because it's currently on-going- I'm in the middle of the meeting. How do we know? Because of the word "now" (and the general context of the conversation.

(2) is a present on-going arrangement for a future event. It was arranged a while ago and hasn't yet happened - so again, I'm "in the middle" of the process. But how do we know the event itself is future? Again, because of the adverb "tomorrow". There's nothing in the verb itself that tells us.

Notice that in the original answers I stressed that we were talking about predictions, volition and events that were either present or past.

Each verb expresses its own meaning, and we combine them depending on what meaning we want to express.
So when "not calling her" is a past event, we express it with the simple past. When it's an expression of our volition in the past, with "would" : I decided I wouldn't call her = I decided I didn't want to call her.

That means that in your original sentence "wouldn't" is not possible because time has moved on "Not calling her" is now a past event, and you are no longer interpreted as talking about past volition (what you did or didn't want/intend to do) unless you add "I decided that..." to make it clear.

So in summary: In the first clause, will becomes would because a present prediction becomes a past prediction:
"I know she'll be working late" becomes "I knew she'd be working late".
But in the second clause a present intention "I won't call her" doesn't become a past intention - it becomes an actual past event. Thus " I won't call her..." becomes "I didn't call her".

If you want to change it back to an expression of past intention then you need a verb like "decide" first. Otherwise, the meaning is not clear.