When you say not relevant, is it completely irrelevant? (eg 4 weeks in an accounts office when she wants to work in dentistry is probably pointless, but 4 weeks in an accounts office when she wants to work in marketing might at least offer transferable skills).
With an internship you are looking to build relevant CV skills and network for a future job, either with that organisation or a similar one. So sometimes it is an investment, but that really depends on the quality of the internship and the organisation.
Travelling in to the office is a good plan if (a) the pay makes that cost-effective and (b) there are actually other members of staff there.
Check out the company - is it reputable? Does it have a grad scheme (which would indicate it had a good set-up for bringing in new talent)? Does it have a clearly stated programme for the internship?
She should query in writing (email is fine) whether, if she makes herself available for work on time each day, they will definitely provide paid work. If the answer is it a clear “yes” then in her shoes I would politely reject the offer mentioning that she is looking for guaranteed paid work and cannot afford the risk that they won’t be able to occupy her.
Having any job on your cv is a good thing at this point in your career, and if the internship isn’t relevant then it’s probably not worth the investment of time and the missed opportunity to make decent money.