Spencer’s twin was definitely the one talking to Wren. I’ve created a list of evidence from this scene alone.
1) To get Ezra’s attention ‘Spencer’ says ‘Ezra?’ and it sounded as if she wasn’t sure it was him, even though he is facing her.
2) At first, Wren and ‘Spencer’ are arguing and it sounds like she says 'don’t call me that’, this could be in reference to him calling her Spencer/twin etc. Ezra definitely didn’t interrupt a friendly conversation between the pair.
3) Her outfit is different from the earlier scene with Furey. She doesn’t have the trench coat, the top is slightly different and her signature watch is missing.
4) When Ezra leaves he says ‘Spencer’, and the camera pauses on her face and she sounds disappointed (see image below). This connects with her asking Wren to ‘stop calling her that’.