Learn English – Is ‘sorted ascendingly’ a valid expression

I would imagine she is referring to the number system assigned to the priorities. For her Priority 0, despite arguably being the "highest" along the conceptual scale of priority, is the lowest, as zero is obviously the lowest of the assigned numbers. Since you both are immediately familiar with the numbering, it wouldn't be unreasonable for her to expect you to understand.

I don't have any solid sourcing to back up this claim, save one anecdote. While doing a project on social policy, a friend asked me to give her the "smallest" bill first. I assumed, since we had hard copies, that she meant the shortest one in length, but in reality she meant the one with the lowest assigned number (and hence earliest). Maybe some people think more in terms of labels than properties?

If this was only in one email, have you ruled out it being a typo? I know I mess up terms for orderings all the time.

The particular sentence is a poor attempt at making an example of a sentence that is both grammatical but very difficult to process because of the multiple center embedding.

Spelled out the sentence is supposed to mean:

Women (that men (that girls love) meet) die"

or

"Some girls love some men. Those men met some women. Those women died".

To make it more understandable, just look at one embedding at a time ("Women men meet die." "Men girls love meet women.").

All these are legal (grammatical) transformations. But juggling all the references leads to the difficulty in processing by a person.

A more intuitive example (makes more intuitive sense once separated all out) is:

"The rat the cat the dog bit chased escaped"

which expands more understandably to

"A dog bit a cat. That cat chased a rat. The rat escaped."

Presumably the sausage machine model allows easy processing of such center embedded sentences, so the inference is that the sausage machine is not the best model of processing that actual human brains do.