I wouldn't have her tested for giftedness at this point in time, simply because no matter what the scores come back as I suspect you might always question whether or not she gave the test her best effort and would wander if the scores shouldn't be higher. I'd look at what your immediate goal is (which I think is more challenging work at school?). Testing *is* one piece of information that can be used to advocate for more challenging work, but until your dd has moved past the stage of not showing teachers what she knows, testing alone is most likely not going to get you the accelerated work (plus testing takes time, can cost $, and there's no guarantee that you'll either get the #s you expect or that the school will accept outside testing). What most likely *will* work - and will be most readily accepted by the teachers - is for you to help your dd learn to not play games and hide what she knows, as well as you collecting a portfolio of the work she's done at home.
For right now, immediately now, honestly I'd ignore the games. As long as she's getting attention and seeing that it's possibly bothering you, there's something in it for her (if she's truly hiding what she knows). You can also explain to her simply that if she wants more challenging work at school she has to be able to know the basics and show that she knows them. She may question why (and maybe you can question why inside your head) but don't agree with her question - explain that that is how the system works, and it's important to have that system in place so kids can't fake their way into something that is too difficult for them - explain that she may know but other kids might not.
If you find that some time goes by and nothing's changing, you might want to consider testing. My dd who vision challenges had many of the same behaviors re reading and re saying numbers/letters looked like other things closely related. With reading she really did struggle at times with words she absolutely knew how to read - it had nothing to do with her reading ability, but her vision broke down when she was tired/stressed/etc. I don't think that's what's up with your dd, but it's something to file away in case this becomes an ongoing issue.
Best wishes,
polarbear
