Can sisters wipe over her hijab during wudhu? This issue has been debated by scholars. Some scholars do not accept that a sister can wipe over her hijab during wudhu. 

However, the evidence that Hanabila presented is very strong. Prophet Muhammad (PBUH) did wipe over his imamah. He wiped over his shoes and his imamah and this action is authentic. Shoes and imamah are not just restricted to men. Women wear shoes and headscarves. 

When it is hard for women to take off the hijab because she is outside in a public place then in this case she is allowed to wipe over her hijab. You will make your hands wet and just wipe over the hijab, the whole entire head. But if she can take it off when making wudhu, then she should.