Hi - I also think your daughter is right about the comma, because the text describing who is talking continues after the inverted commas. If it was the other way round I think it would be a full stop as it closes the whole sentence (Mr Fox whispered to himself, "All is safe! The boy is sound asleep.")
Any English teachers out there???
I found some (rather lengthy!) information on this for you in Wiltshire.ac.uk which seemed quite good. Also try oxforddictionaries.com. In my youth I always used "Plain Words" by Ernest Gowers as my grammar/punctuation bible but can't currently lay my hands on my copy!
Anyway here is the stuff from Wiltshire.ac.uk. It has some exercises and answers at the end which may be useful:
Skill: Speech Marks
We put all spoken words in inverted commas (also called speech marks or quotation marks). They show that someone is speaking. Single inverted commas are usually used
'What is your name?' she inquired.
But double inverted commas are also acceptable
"What is your name?" she inquired.
The first inverted comma is put before the first spoken word. The second inverted comma is put after the last spoken word. Only one set of inverted commas is put around each passage of spoken words, even if it includes more than one sentence.
He said, 'My name is Harris. I want to see Mr Baker.'
We put the inverted commas around speech after any other punctuation mark. Note that the inverted commas at the end of speech come after the comma, full stop or question mark.
'Are you the gentleman who called earlier?' she asked. 'Mr Baker asked me to see you.' 'I would prefer to talk to Mr Baker himself,' the man replied. 'I am afraid that he is out.'
We begin each spoken sentence with a capital letter, even if unspoken words introduce it.
He said, 'Have you any cornflakes?'
The spoken sentence is 'Have you any cornflakes?' It is introduced by the unspoken words, He said, which are part of the same sentence, but Have begins with a capital letter as it is the first word of the spoken sentence.
She answered, 'They are on the shelf behind you.'
Here the spoken sentence, 'They are on the shelf behind you' is introduced by the unspoken words She answered. They begins with a capital letter as it is the first word of the spoken sentence.
When unspoken words interrupt a spoken sentence, we do not use a capital letter at the point where the spoken words continue (unless the word is the personal pronoun 'I', or a proper noun like 'Joe', 'Leeds', 'Mr' which always start with capital letters).
'They are not,' she said, 'going to see the film.'
Here the spoken sentence is They are not going to see the film.
Its first word, They, begins with a capital letter. The spoken sentence is interrupted by the unspoken words, she said. When the spoken sentence continues, the first word, going, does not begin with a capital letter.
We always divide spoken words from unspoken words by another punctuation mark, as well as by inverted commas.
The punctuation mark may be a question mark:
'Have you permission to be in here?' the guard asked.
or a comma:
The first man replied, 'No, I'm afraid I haven't.' 'We didn't know we needed anyone's permission,' said the second.
or an exclamation mark:
'Get out at once!' the guard shouted.
If the spoken sentence continues with unspoken words, we do not begin the unspoken words with a capital letter.
'Have you anything to say to me?' he asked. 'Go away!' shouted the girl, trying to shut the door.
We begin a new paragraph when a sentence includes the words of a new speaker.
Bill was walking along the corridor, thinking of Saturday's football match. 'Hey!' called Sally. 'Mr Morgan is looking for you.' Bill asked, 'What is the matter?' 'I do not know,' she replied. 'He looked very angry. What have you done?'
Exercise: Rewrite the following sentences, putting in any capital letters and punctuation marks that are needed.
Hello said the policeman what do you think you're doing?
I am trying to open this window said the man
Is this your house? asked the constable, thoughtfully
Yes it is answered the man I have locked my keys inside
It's a very warm night to be wearing gloves our eagle-eyed copper then suggested
I get chilblains retorted the man
What a shame exclaimed the policeman I would like you to accompany me to the station
I am sure said the man that you could find it yourself if you looked hard enough
Would you find it easier to talk if you took the stocking off your head first asked the policeman now come along with me
Answers 1. 'Hello,' said the policeman, 'what do you think you're doing?' 2. 'I am trying to open this window.' said the man' 3. 'Is this your house?' asked the constable, thoughtfully. 4. 'Yes, it is.' answered the man. 'I have locked my keys inside.' 5. 'It's a very warm night to be wearing gloves.' our eagle-eyed copper then suggested. 6. 'I get chilblains.' retorted the man. 7. 'What a shame!' exclaimed the policeman. 'I would like you to accompany me to the station.' 8. 'I am sure' said the man, 'that you could find it yourself if you looked hard enough.' 9. 'Would you find it easier to talk if you took the stocking off your head first?' asked the policeman. 'Now come along with me.'