Women wearing tall hats for the purpose of adornment

 If she wears it for the purpose of adornment among other
women or her mahram relatives, that is subject to the condition that it
should not resemble the dress of men or of kaafir women. But if she goes out
wearing it in front of non-mahram men, this is a kind of tabarruj (wanton
display), and Allaah says (interpretation of the meaning):

“and do not
display yourselves like that of the times of ignorance”

[al-Ahzaab 33:33]

“Everything which involves
wanton display or makes a woman stand out among other women in a manner that
involves beautification is haraam and is not permissible for her.”