Who is the subject(doer)? (There, she’s said it)

Question

There, she’s said it.

1- Could you tell me please who the subject(doer) in a sentence like above is?

• The last subject or questioner(in this case David)?
• The others(all the peoples who are present there)?
• The subject is uncertain?

2- What does refer it to?

3- What's the meaning of there here?

The full text is:

It seems to me,” Henry says, in his slightly pompous way, “that if this is a murder, it would be almost impossible to solve. It seems to have happened in the middle of the night. We were all asleep in our beds. There are no witnesses. Unless someone wants to confess, or share some helpful information about seeing someone creeping about in the night, I don’t see that there’s much to go on.” Beverly listens to him, licks her lips nervously, and waits. No one else volunteers anything. Finally, she blurts out, “There’s something I should probably say.” All eyes turn her way. She almost loses courage. She doesn’t know if the argument between Dana and Matthew is relevant or not, but it will certainly sound damning. “What is it?” David says calmly, as she hesitates. “I heard them arguing, last night.” “Dana and Matthew?” David says, as if in surprise. “Yes.” “What was the argument about, do you know?” She shakes her head. “I heard them shouting, but I couldn’t make out any words. Their room is next to ours, on the same side of the hall.” She looks at her husband. “Henry slept through it all.” “What time was this?” “I don’t know, but late.” “Did it sound . . . violent?” David asks. “I don’t know. It was just raised voices. No crying or anything. Nothing slamming, if that’s what you mean.” There, she’s said it. If Matthew’s done something wrong, then it’s good that she’s told them.

Answer 1

The subject in this sentence is the person referred to by the pronoun "she" -- in this case, this is Beverly. I'm not 100% clear on your thought process, so it's difficult to provide much guidance on how to identify this beyond the fact that "she" is a nominative pronoun and is in the typical position for the subject of a sentence.

As for "it", this refers to what she's just said, and harkens back to her earlier line:

There’s something I should probably say

What she just said, that Dana and Matthew were arguing, is the "something she should probably say".

Answer 2

Let's say that I warn you that an heirloom I'm handing you is fragile and that you should take care when examining it. As you take it from my hands you get an incoming tweet on your mobile phone, which you are so eager to read that you fumble the hand-off and drop the heirloom on the floor where it smashes into bits. I might say:

There, you've gone and broken it!

There is an exclamatory reference to what has just transpired.

Answer 3

In spoken English and not written English, the word "there" placed at the beginning of a sentence like yours refers to the expectation of the speaker that the other person will do or say something that the speaker expect him or her to say. The fact this narrator uses it suggests she is telling the story aloud. Even if, in fact, she isn't. It mimics speech.

It is a spoken form usually. However, in your text, the author is referring to what comes earlier in the text. Here, it seems to refer to the fact that Beverly is telling the others what she heard. The there comes from the narrator telling the story.

"There, I have explained it to you." (I can say to you now here.) There refers to the entire explanation.