Assuming she has graduated from high school, if she had been experiencing significant cognitive processing issues prior to graduation, your local public school would have most likely already conducted a special education evaluation which would have included cognitive processing. If she has not yet graduated from high school, that would be the best place to seek an evaluation at no cost. If she has graduated and is enrolled in college, most colleges and universities offer such evaluations. If none of that applies to your situation, you would need to find a local clinic in your area that performs educational evaluations.