I'm not 100% certain, but I think you need an entry clearance to enter on a work permit period.
If you're not handling her immigration paperwork, I'm surprised you didn't run this idea past the person who is who could explain the consequences in more detail to you.
But when it boils down to it, getting the clearance once the permit comes through most of the time will add less than two weeks to the process.
Considering the consequences, doesn't seem like a good idea.
Immigration law in this country is not something to wink at -- not ever, but especially not now that the penalties for violations have gone up drastically in their severity.
ETA: It doesn't make a difference if the internship is unpaid, btw. No work means just that. You even need a special visa for volunteering.