Removing girl from difficult background- finding it hard where colours are similar, any suggestions?

Topaz remask is a really useful plugin

Yes Photoshop is not magic you need to develop knowledge and Photoshop skill. When you can nor find some way to develop contrast between the subject and the background it is difficult to separate the two.  When it is impossible you need you brain and your Photoshop skills you got work to do. The image noise does not help,