London is the only center I am aware of that routinely books medicals without a 2NL. They are shameless about it too, there are people who didn't realise the medical expires that have actually had them expire before interview...
I wonder why Dalia's experience is different to what other OCers have described? Every other case other than London I have heard of, people have reported requiring the 2NL to book the medical. Because the main business of these doctors is often visa related, it's normally not an issue to find family bookings, it's not like each person has to have a completely separate exam slot/room as would be the case for 4 or 5 strangers.