Is it something organised through her university course? If so, then she may be able to do the day a week during term time, as long as she's not timetabled for lectures or seminars on that day. It would be completely inappropriate to miss scheduled classes for a work commitment.
I've had student research interns at my place, during term time, as we arrange the post around a number of hours, so I had 75 hours over 6 months, which the student managed very well. They're paid a basic hourly rate to do interesting but relatively basic support work for my research - doing bibliographic surveys, readying materials for digitisation - that sort of thing. Stuff appropriate to 2nd or 3rd year undergrads. It gives me some much needed help, plus they get experience working with a top researcher & they get my support & mentoring. I read one student's UG thesis (he's now doing a PhD) and discuss career possibilities etc.
That's a scheme within my university. Another place I worked at gave students the opportunity to pitch for a pot of money to support them in doing unpaid internships over the simmer vacation. For students who need to earn over the summer to fund the next year's study, this was a good scheme.
Nowadays I think there is much more regulation of internships - I gather none of them should be unpaid? Or if they are unpaid, they shouldn't be replacing a formerly paid role.
But if it's a good internship, it's very valuable.