yitay: Re: The A”H. Covering hair is not erva by an unmarried woman, hence the difference between covered hair (by an eishes ish) and something that even unmarrieds should cover due to erva.
This is completely incorrect. The determining factor is whether the girl is still a Besulah, and has nothing to do with Keddushin. Hence a woman who gets married in many communities does not cover her hair during the wedding itself.
Source: Chelkas Mechokek (also Bais Shmuel) SA AHZ 21:2.