I will think twice before I post to a similar topic about "should I, shouldn't I" report someone - I'm more than likely to suggest to the OP to please not ask for opinions, but to just go away and validate their facts, and then decide for themselves.
I know the OP has come back and said she doesn't believe her friend's story so this is less relevant than it was, but I think this is a sensible approach.
The benefits system in this country is massively complex. Who can claim what and how much is often misunderstood mostly by people who haven't ever claimed, but also by people who are claiming and surprisingly often by the people who are administering the claims. There is already at least one misconception on this thread and there are many others in the public domain.
Even the DWP admit that the number of fraudulent claims is small and the majority of claimants who are investigated are found not to be making fraudulent claims. I suspect most of those will be made by people who thought they were 'doing the right thing' but whose idea of fraud was based on their own misunderstanding.
Some on here will think this is fine, after all 'what's the worst that can happen'. But unless it's a routine compliance check they can and do stop your benefits and any related benefits. And we're not talking a system that works in days here, it can take months. Meanwhile, there's no food in the cupboard and you're building up rent arrears. If you're lucky you'll still have a roof over your head and your landlord won't kick you out.
That, IMO, is why MNers advise people not to report unless they are completely 100% sure. It's not because they think that the people committing fraud should get away with it.
In my case, after 5 months I was reduced to going down to the job centre and literally begging someone to do something because despite almost daily phone calls to DWP I had £2.50 left before I reached my overdraft limit, the rent was due the following day, I had one tin of beans left and I'd just put the last 50p in the electric meter. It took a further 8 weeks to get the HB reinstated.