If she gets married, joins the military or becomes "emancipated" she can move out. To become emancipated she will need a lawyer to file some paperwork and she will have to go to court. She has to show the judge that she can support herself. She will be 18 in a few months. Then she can move out as she is an adult under Texas law at 18.
I recommend that you consult with an attorney regarding this matter.
Instead of moving out and becoming broke, isolated, losing her future prospects and the support of her parents she should go to counseling with her Mom to work out the issues.
A baby is a huge responsibility and she needs her parents more than she realizes.
Having a new baby at that age puts her at risk for a life of poverty. Part of growing up is learning to accept with maturity disagreements with loved ones.
Unless her Mom is abusive then in the long run staying with her parents is probably best for her and her daughter. Yes it is hard but welcome to life.