Oh, okay. Well, this is not so bad. There are options, but that's probably not the best one.
When you say you had the same problem e-mailing the RTF, did your friend just upload that file to CreateSpace? It probably was the same page size, although the bigger problem would be that you're then dependent on CreateSpace's (i.e., a computer's) idea of formatting. You would need to do something first to change the page size, which would require your friend to read the RTF file into Word or OpenOffice for Windows. The best option would be for her to go to CreateSpace and download the .doc template for a 6x9 file, then open the template in Word. I think it comes with instructions. If she doesn't have Word, she can download OpenOffice for free. The process is essentially the same.
Follow the instructions if they are in the template.
If not, the basic task is to select any text in the template, go to the Insert menu, choose File, then your RTF.
Save the file.
Go through the file to check it, applying formatting if needed, then save it as a PDF file. On a Mac, you choose Print, then PDF. I assume Windows uses something similar (Print to PDF, I think).
The results almost certainly will not be perfect, but the PDF should be the right size.
If all this is clear as mud, talk to your friend (to get a sense of how comfortable she is with Word) and write again. I'm signing off for the evening, but I will check tomorrow AM.