Under Texas child custody law can a grandparent petition for full parental custody

You need to answer some questions: a) whether the biological father is deceased; b) whether the biological parents had a CPS removal of the kids; c) whether there is a substantial risk to the safety and welfare of the child at issue so that "the child's present circumstances would significantly impair the child's physical health or emotional development; or both parents, the surviving parent or the managing conservator or custodian either filed the petition or consented to the suit." If the answer is YES to the last elements, then you might have a chance. If CPS is involved, cooperate with them and make your intentions known. Try to get your daughter's consent to the custody.