Mention to her DO NOT discuss this with anyone who is not a lawyer. This is conduct which can have very serious consequences in terms of both criminal consequences and collateral civil consequences for her applications for college, employment, loans etc... Consult immediately with an experienced TX defense lawyer, who can properly advise her under the protection of the attorney-client privilege. Handle this right at the start with an attorney for her.
Since she is considered an adult under Texas law, there is no requirement that she bring her parents with her to her court dates. She may be entitled to a court-appointed attorney but she will have to prove her income and bills to show that she is indigent and get that free attorney. If she does not qualify, the court will give her an opportunity to hire an attorney. Many courts will encourage her to represent herself and waive her right to have an attorney represent her (especially if she doesn't qualify for the court-appointed attorney but can't afford to hire her own lawyer). I would strongly discourage her from doing so; she is not a lawyer and the prosecutor will not be trying to help her (that is not the prosecutor's job).
Regardless of the fact that she may be considered an adult under the state law, its been my experience that most judges like to see parents come with a young defendant like her, so they know that the adolescent's parents are aware of their arrest and are going to do something about it within the family.
As Mr. Brinkmeier aptly said, hire a lawyer for her now and it may have a positive impact upon the rest of her life.