Add an existing SkyID to my account?

Hi All

(Sorry if I've got the wrong board)

I recently signed up for Sky Go and wanted to add my daughter as a secondary ID on my account, so she can watch using my subscription (she lives 200 miles away so can't just use my TV!)

The problem is she already has a Sky ID for broadband so when I try to add her the computer says her email is already registered.

Does anyine know how I add an existing Sky ID as a secondary on my account?

TIA

ADG