commas - Punctuation of direct speech, edge cases

I recently learned that I have developed a consistent, but entirely wrong approach to punctuating direct speech in fiction. I am in the unenviable position of trying to relearn.

Previously I wrote such things as:

"I'm done." She said.

when the quoted speech was definitely, absolutely the end of a sentence. So now I know I need.

"I'm done," she said.

This follows the rule that a period is only allowed when the end of the spoken sentence is also the end of the sentence in the narrative. For example:

"I'm done." She slammed the door on the way out.

So, it now looks odd to me when there are multiple sentences in the speech:

"I can't take her. I'm done," she said.

Can you reassure me that is correct, or give the correct form? Please don't suggest rewriting the sentence to put 'she said' in the middle - I'm aware of that: I'm specifically asking about the punctuation rules.

The other odd case is speech ending with an ellipsis. Do sentence terminating ellipses (four periods normally) become:

"I can't take her. You know, ...," she said, nodding towards Jane.

If so, are non-terminating ellipses dealt with the same way?

"I can't take ...," she nodded towards Jane, "any more!"

or can non-terminating ellipses be used unadorned?

"I can't take ..." she nodded towards Jane, "any more!"

I'd be very grateful if you could point me at references as well as answers. For the record I am a British writer writing for both British and US publication, so any variation is also interesting to me!

Answer

The only thing you have to "relearn" is that a full-stop at the end of reported speech becomes a comma when the sense runs on into the sentence which reports it.

"I'm done," she said.

That's one complete sentence reporting some speech.

It doesn't matter if what is being reported has its own sentence structure: that's contained within the quotation. It's the comma at the end which links the quotation to the reporting. Please be reassured that your example is correct:

"I can't take her. I'm done," she said.

Where you're reporting a trailing-off of speech, or some other ending, the punctuation mark isn't a full-stop so it doesn't become a comma. However, because the sense runs on into the reporting clause, that doesn't get a capital letter, in much the same way as the first example.

"But I thought he was..." he complained, lapsing into silence.
"Oh sh—" he whispered, seeing the car hurtle towards him.
"No!" she exclaimed, slamming the book shut.

Where an interjection interrupts the reported speech, I'd use a dash. There's no punctuation at all at the end of the first fragment, because there's nothing there in what's actually being said.

"I just can't" — she sobbed ostentatiously — "take any more!"