Unfortunately you've learned the hard way that you can take nothing for granted when it comes to placement tests.
A WISC-IV test is so basic that a 7 year old can do very good on yet have only limited math skills. Their is also a very good possibility that the school isn't teaching her math in the same way that she was tested. It is completely possible that a child could be taught only basic math in terms of add/subtract/multiply/divide and have no word problems at all. If that child was then given a test that was 100% word problems they could very easily just freak out and get none right... not because they were stupid but because they were given something they had never been exposed to before.
Working with her on your own might be the best way forward in math as it would appear that what the school teaches in the elementary grade isn't what they test later on.
If being in the advanced programs is very important to you then why not hold her back instead of skipping a grade... there is nothing wrong with a child not finishing school when they normally would... not to mention there are other issues you will have to face when you push a child to skip grades - social issues like a lack of friends, not fitting in, being small.... you have a great reason now not to skip a grade and it would give you a lot of time to prep her for the math test she would then take again.
