How Do I Report Benefit Fraud Without Knowing Address Or Ni?

I know this young woman who is currently claiming benefits for something to do with anxiety, but with the money she gets paid, she uses it to go out clubbing, pay for her free house, a free car and she’s booked a holiday and even offered to pay for my partner to go away (she of course, refused). And now she’s got knocked up and boasting how much the “government” will pay for everything. I really want to report all this to the DWP and have them investigate how much they’re wrongfully giving her, but the online form asks for information I don’t know, such as her National Insurance number, her full address etc…
What can I do? It doesn’t seem fair that she can get away with this…