Can be sentences turned into questions just by changing intonation in spoken/informal English?

Question

There's a sentence:

She doesn't want to go with us.

How would you use this as a question to specify the cause? Like:

— Would you like to join us?

— No, I will stay at home today. My girlfriend isn't letting me go.

— Why? [question to specify the cause]

From watching TV series I was sure that we can just say:

— Why? She doesn't want to go with us?

But my friends tell me that I should use

— Why? Doesn't she want to go with us?

I feel that saying it like this asks the wrong question, like asking if she wants to go with us, but being uncertain that she will agree (my first language is Russian, and it can be done there). I also can't find anything to support my point of view, hence is my question.

Answer 1

Raising tone on a statement to phrase it as a question can be done in conversation, but it's clearer to phrase it as the final quote.

"She doesn't want to go with us?" implies surprise, as if she's expected to want to come, and may therefore be considered rude dependant on context.

Answer 2

Yes, what you have observed is normal for informal spoken English, at least in the northeastern US dialect I speak. (And, I think, for many others as well.) Your friends are correct about formal, textbook English, though.

Asking a question without changing the word order usually does imply either surprise or confirming a fact, whereas using standard question word order is more neutral. For example,

Standard question word order:

Customer: I would like the salad, with nothing on it.
Waitress: Do you want salad dressing?

This feels like a neutral question, simply asking for a yes or no answer.

Statement word order:

Customer: I would like the salad, with nothing on it.
Waitress: You don't want salad dressing?

This feels like the waitress is specifically asking the customer to confirm the statement "You don't want salad dressing."