If your daughter is your dependent, then the costs of the rehab facility are a deductible medical expense. (If you provide more than half your daughter’s support but your daughter is not your dependent because her gross income exceeds the $3,700 limit in 2011, you can add her medical costs to yours.) You must itemize deductions in order to write off medical costs; only amounts in excess of 7.5% of your adjusted gross income are actually deductible.
Your travel costs may or may not be deductible. Travel costs to accompany a child who needs medical care and to visit a patient if the visitation is recommended as part of the treatment can be deductible. It’s up to you to show that your travel with her and your costs to visit her were medically necessary and not just your personal choice.