My mother wouldn't let me wear a miniskirt.

Literal

Mother [topic-は] I [subject-が] miniskirt [object-を] wear [nominalizer-の] [object-を] did-not-permit

ミニスカートをはくのを許さなかった = 'did not permit wearing a miniskirt.' はく = to wear (lower body garments: skirts, pants, shoes). 許さなかった = negative past of 許す.