All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If you know that your wife will pass by any men even on her way to that place or when returning from it, then it is not permissible for her to go out wearing perfume; for more benefit, please refer to Fatwa 84119.
However, if it is known that she will not pass by any men, like if you drop her off to that place of event (women's gathering) and it is known that no non-Mahram man can smell the perfume that she wears, then it is permissible for her to go out wearing perfume in this case.
Allaah Knows best.