My friend is travelling to visit and she forgot to inform them about the bassinet request. will the check-in counter automatically allocate the bassinet seats to her plus a bassinet, when they see her with the baby? or does it need to be prebooked in advance?

When she checks in, she may request for a bassinet seat if it is still available. Otherwise, the airline will provide an infant seatbelt. It is ultimately safer to pre-book the seats.

You can request for the bassinet at the check-in counter but it will not be confirmed as it's based on first-come-first-serve and there are limited number of bassinets onboard.

It should be prebooked. You can ask her to check with airlines stuff upon checking in to see if there is any more front seats for bassinet.

thanks