I am Under 16, do I need to be there in person or can my mum just bring my pport in to get an Oyster Card..

I live in America but spend a significant amount of time in England over vacations. I am under 16, a British citizen. My mum is going over to London for a while soon, and i'm not... can i get her to just bring my pport to get my oyster card or willi have to be there in person?