I would talk to your school district's gt department and find out whether they accept outside testing. If they will, find out what test(s) they will consider -- though WISC is probably a safe bet if they do. Our school district uses CoGat and NNAT but it's my understanding that they will consider outside testing. Some school districts only use their own testing. If you are in one of those districts, you may want to save your money unless you have other reasons for testing.
Good idea, I will call them and ask. We live within driving distance of the GDC so I am considering using them and they are probably quite reputable with the school systems here. No other reasons for testing, she's a pretty cut and dry mildly gifted child in my opinion and just want her to qualify for the G&T program.