[LeRich]

Your situation is extraordinary as most private rental landlords are in the game to make a profit. Though you haven't mentioned how much the rent / mortgage is, as you're paying interest only, I would assume the rent Emily pays is far lower than market value. I also assume the license is not annual if the council are charging £900. You are liable for the cost as long as you are landlord so you'll have to suck up the cost yourself unless you pass it on to your tenant, which I would say is reasonable to do in this situation.

You might alternatively seek to cover the cost by changing the nature of the tenancy and getting a second person living there, subject to Emily's agreement and there being a second bedroom.