Shaykh Dr Zaid Alsalami is an Iraqi born scholar, raised in Australia. He obtained a BA from Al-Mustafa University, Qom, and an MA from the Islamic College in London. He also obtained a PhD from ANU, Canberra. He has written and translated several Islamic texts and also prepared educational videos on Islamic rulings and practices.
If the husband has allocated this money exclusively to his family, and for the wife to spend it on their household, then no, she cannot spend it on other things. If the husband gives his wife money, without specifying, then she can do with it what she wishes.
However, it would always be best for her to consult with her husband, and for the husband to honour his wife's family by financially assisting them within his capacity.
And Allah knows best.