Although Edwardian women were not bound by the same strict rules as their Victorian sisters they still had a reputation to guard.
Ball gowns themselves were extravagent floaty affairs reaching to the floor cut to emphasise a small waist or later the S shape.
Nearly all studio photographs you will see will be of the head and shoulders which for young women was where the main emphasis lay.
A ball or dance was one of the only occasions it was totally acceptable to have a bare neck and shoulders. The neckline could be very low but a small posy of flowers was worn at the lowest point to obscure any view of a cleavage. This fashion even had a name décolletage
These occasions were very important if she was seeking a suitor .
Any single woman who wanted to attract the attention of an eligible bachelor
needed to strike a balance between looking alluring and being considered "fast" or desperate. It is no different for the girls of today.
They had to choose how low to go and what to show.