Oh man, that sounds hard, hard, hard but glad that you're seeing light at the end of the tunnel and FWIW, I would take the sleep school option even if you might not need it by then and treat it as a bit of a holiday - you bloody deserve it.

I to am wondering if the issue is with her room (rather than sleep as such) and also if sometimes Dp is not there when she goes to bed but then she can hear him later so gets up? So perhaps to her, it is worth getting up after a few hours sleep cos Dp might be there? Dunno. Maybe the day sleep is not so much of a problem because she knows that Dp isn't around during the day so she's not going to miss anything.

I am sending you a virtual bottle of scotch and a funnel!