The designer liked my work and contacted me herself. She works with 3 different photographers to get consistency in her presentation from what I understand and as a result has put up notices she's not interested in free collaborations anymore. She sometimes insists on being on the shoot and sometimes I have to go up to Leeds to see her and shoot there.

I assume you can buy her stuff and use it to photograph it, but I doubt she'd be willing to give out stuff for free under similar conditions as she lends me things since she's restricted collaborations so much... I met her when she was just starting out so I was lucky. It's easiest to find starting out designers by going to fashion collages or looking on sites like here or modelmayhem than approaching somoene that already has a stable team...