In the line of dialogue: 'Yes, but she wasn't even there, was she, according to you,' where, if anywhere, should the question mark go?

These ones always stump me, where the question is embedded in a non-interrogative sentence.

I would definitely say: 'Yes, but she wasn't even there, was she, according to you?'

But that might be completely wrong!

This always confuses me too. As the sentence currently stands I would place it at the end.
Alternatively, you could have the line as a statement: 'Yes, but she wasn't even there, was she - at least according to you.'
or a question and a statement:
'Yes, but she wasn't even there, was she? - at least according to you.'

I wouldn't use a question mark at all - it definitely reads as a statement to me.

Dee