Oh man that is so hard. I guess if it were me I would pursue the testing and at the end regardless of what happens put her into a different setting either the GT program, if you think it is a good fit, or mabe a different school's GT program or a different school with independent study. I would just make sure she understands that she is very smart and that something is going to change for her so she is not so unhappy and stuck in a situation that is affecting her self esteem.
If you do the testing I would tell her she did very well and that you are looking into a few different options to help her find a better fit. (regardless of the results). It sounds like where she is at now is not going to work with or with out the testing.
