It depends a lot on your DDs individual personality and circumstances, and how much financial support she would be able to get from you after uni in the early stages of her career.
Presumably shes wanting to do this course because she is hoping to pursue a career as a writer. In which case, what sort of writer does she want to be?
Assuming that what she is currently writing is "very good, considering the author is only 17" - (I have no knowledge of her actual talents of course) - it takes years and years of writing stuff which she will later agree was never publishable, but gradually improving, before she can write stuff that is actually properly good. If she wants to be a really good writer, she will either need to have an independent source of income (e.g. you) to support her while she writes unpublishable stuff for years, or she will need to have another income stream e.g. a career.
If she can rely on independent support, then there is no harm in doing a creative writing course, it can't hurt. If she is going to need a career to support herself too, she would be better off chosing a degree course which will facilitate that, preferably at a uni that will allow her to do some modules in creative writing. Journalism is obviousy a very good complementary career but there is lots of competition for that and she maynot get anywhere. There are a lot of less glamorous jobs which will both draw on and help improve her writing skills that she could look at, e.g. in publishing houses of academic journals and doing in-house copy-writing for various big organisations,
However, it is sadly true that writing that is "good" is not the same as writing that is "popular". Very few authors that are Booker Prize level contenders are millionaires, and very few authors who are millionaires actually write anything of literary merit.
If she is more interested in writing for the more lucrative end of the market, and has no ambitions to create great works of literary art, then the creative writing course will be likely to be very helpful, as it will certainly teach her how to understand and reproduce popular formulars to have mass appeal. However, there are a lot more writers trying to make a living at this end of the market than there is income available from this market. The lucky ones who do successfully make a living are the ones who are also good marketeers - so she would benefit from getting some understanding and experience of martketing if she is going to succeed here.