How will my Placement Year salary affect my mum's benefits and rent?

I'm going to start my placement year in July and I will be living at home with my mum and earning about 20k for a year in industry. I'll obviously still be classified as a full time student because this is a part of my course but it also means our household income will change. My mum is completely on means-tested benefits and we live in a council house so I was wondering if/how my placement income would affect that as I would be getting a salary from work but still be classified as a full-time student/dependent. If anyone knows about this or has gone through this before, any input would be appreciated! I've obviously contacted UC about this but would like some idea of what to expect before they get back to me, cheers!