Right so.. abit of a talk to up

My mum applied for EEA(PR) about 2 weeks ago, application included me and my sister, anyway she received a confirmation email today(great news). Problem is she moved maybe a week after the application was submitted. Now in the email it says to fill out this form incase of changes or circumstances.. https://www.gov.uk/change-circumstances-visa-brp
However, she doesn't have a digital copy of her passport, or my sisters. I happen to have a scan of my mine. Also I don't understand the bit about people who shouldn't use this form.. "If you’re an accession state worker or in the UK under the Workers Registration Scheme (WRS), you do not need to notify us of an address change." She was registered WRS in 2008, she no longer works for an employer.
I'm not sure what we should do to change address? Would a written letter, explaining the situation and maybe including my passport photocopy and explaining how the application was applied together, suffice?