Depending on what county you believe she currently resides, I'd Google a police department number for an abuse hotline and call it in.
Pay phone?
http://www.ice.gov/news/releases/1009/100928dallas.htm
copied from that page:
"
The cornerstone of the DHS Blue Campaign is to identify potential human trafficking victims, empower them to seek help, provide information and referrals, rescue them from their traffickers and connect them to services and support that are available to them. ICE is making every effort to prevent human trafficking in the United States by prosecuting the traffickers, and rescuing and protecting the victims. The greatest challenge facing law enforcement in the fight against human trafficking is victim identification. Therefore, it is key that the public be educated about trafficking to recognize and report the potential victims that live and work among us.
If anyone knows or suspects someone is being held against their will, ICE strongly urges them to contact the ICE tip line anonymously at 1-866-DHS-2-ICE.
The public may also call the National Human Trafficking Resource Center's toll-free hotline at 1-888-373-7888."
No idea if this is an anonymous tip line or not but anyone calling a toolfree number should understand and be forewarned that part of the tollfree system is the delivery of the phone owner's information to the owner of the number called,
Since that is all of North Texas it is probably the best number to call.
And if the pimp moves her from state to state then he crosses state lines and that means even more penalties for him.