Learn English – “survived by her partner” meaning

Yes, that's right. The author is trying to make you feel what the viewpoint character feels by describing her physiological reactions to fear, rather than simply telling you she was afraid.

This sort of thing is very common among writers who follow the mantra of show, don't tell.

In general, "such was the [noun]" or "such is the [noun]" are used when you want to indicate that the description of the subject is coming soon or has immediately preceded.

In this context, "such was her astonishment" at the beginning of the sentence is pointing to the description of her astonishment that follows. For clarification, remove the middle part of the sentence to make this connection easier to see:

"Such was her astonishment that she leaned against the wall, incapable of making another move."

"Such was" can be used in this way after the description rather than before it:

"She leaned against the wall, incapable of making another move. Such was her astonishment."

In this case I moved "such was her astonishment" to a new sentence after the description of the astonishment.

Here is an example of the same structure used in a different sentence:

Such was the force of her presence that what came after her was defined in terms of her absence.