I would like to know the age a child can sign theirself out or a parent can sign them out of high school. We've asked guidance counselers and they have not replied they do not want my daughter to drop out.

Here is a link with explanations:
http://www.washingtontimes.com/news/2012/apr/5/house-bill-increases-age-to-leave-maryland-schools/
The current dropout age is 16. It will go to 17 in 2014.
If she drops out of high school, I do hope she can marry a man with much, much money. Her odds of ever working a good paying job with no high school diploma are slim and none. Even college grads now only have a 50-50 chance of finding a job! I wish you the best of luck, and hope things work out where she will stay in school.
I don't want your daughter to drop out either. A high school diploma is the first thing to start a life with.