reserved and modest
demure - modest
A ‘demure’ person is considered to be quiet and well-behaved. They are not necessarily shy but instead humble and unpretentious, meaning that this word has been used historically to express approval, particularly towards women who behave in this way. In more modern times, however, it may cause offence to refer to a woman as such, and demure people are thought to be boring by some.
Our boss is quite old-fashioned. He expects women to be demure and compliant rather than confident and assertive.
On the outside, my grandmother may appear to be the epitome of demureness, but she is actually a very boisterous character.
The function is expected to be a rather sedate, reserved affair, so Claire decided it was best to dress demurely.