It probably doesn't matter that much. As a retired physics teacher I've always encouraged those who are capable to do triple science - if for no better reason than it seems a waste of talent to do otherwise.
On the other hand, I would always support a young person's right to self-determination. Presumably, if she's making her GCSE choices, you DD must be 14 or nearly, so she's at an age where she can picture her future self and wants to make her own decisions as to how to get there. As others have said, you can only advise.
I have no direct experience of media (or media studies). I imagine it could be just as rigorous as any other subject, although I have noticed that it tends to be chosen by less motivated students. Of course, that may be a grossly unfair observation generally but it might mean your DD could find herself in a group who would take the work less seriously. Only she will know if that is likely to be the case.
I do, though, wonder how important any subject (other than English/maths) is at GCSE. As an example, DS2 took only 8 (I)GCSEs (all the school would allow) and then did maths, physics, and music technology at A level. He now has a very senior job in IT/computing despite having never studied it at school.
From your list, it looks as if she could do triple science and music. Would she consider this? irregularegular makes a good point about the amount of coursework many of the less scientific subjects have, and people who are scientifically trained tend to be pretty versatile so she could still end up being creative but with more choice if she took a more scientific route.
And, of course, engineering is one of the most creative subjects there is!