Daffy's advice is sound.
It is a phase all girls go through, so you are not alone!
Your partner may fel extra pressure as a 'non-biological' parent, so you must help to bolster his elf-esteem during this time, as well as backing all his discipline decisions - if you think he is wrong, talk to him alone afterwards, but back him in front of your child.
During times when you are all having a good time, point it out verbally, how nice it is when everyone is nice to each other, and how you all enjoy being together. You should each take time to assure your daughter that you love her and are proud of her - she will be going through periods of doubt and low self-esteem, which manifest themselves in slks and moods. When you ask her what is wrong and she says she doesn't know, don;t get frustrated - she is telling the truth, she doesn't know, you have to read between the lines a little.
Make sure you each take time to give her some individual attention and time, and that you each affirm her as a good person whom you love a lot.
Beddtime is still a good time to kiss her good night, and tell her you love her - I still do this with my youngest daughter, and she is twenty! We are never too old for a cuddle and some reassurance.
It is a tough period, but be patient, she will re-join the human race eventually - they all do!