My 17 year old has significant unearned income from unemployment. If I claim her as a dependent she will be subject to my tax rate which is around 30%. It makes more financial sense for her to claim h

If she is your dependent, you can elect to not claim her, but she still would need to file as a dependent. 

You can't simply "allow" her to claim herself, the IRS would not allow that. 

A “Qualifying Child is a person that meet these tests:

• WHO IS THE PERSON? The person must be your son, daughter, stepchild, eligible foster child, brother, sister, half-brother, half-sister, stepbrother, stepsister, adopted child or a descendent of any of them.
• HOW OLD IS THE PERSON? The person must be under age 19 or, if a full-time student, under age 24. They must also be younger than you (or either you or your spouse if you’re filing Married Filing Jointly)

There is no age limit if your child is permanently and totally disabled.

• WHERE DOES THE PERSON LIVE? The person must have lived with you for more than half the tax year, but several exceptions apply such as school and military service.
• WHO SUPPORTS THE PERSON? The person cannot have provided more than half of their own support. It doesn’t matter how much they earned.
• HOW WILL THIS PERSON FILE THEIR TAX RETURN (IF THEY HAVE TO FILE ONE)? The person can’t be filing a Married Filing Jointly tax return, although there is an exception to that.