I don't know why I didn't realise that I hadn't made it clear that the shop girl could neither see, nor be seen, due to being under the counter and hidden from view. It's so obvious now. Duh. I did write 'А внизу, под прилавком, Алина была невидимо.' later on, but that is a long way after the doorbell rining, I guess I should have put it in earlier.