My name is XXXXX XXXXX I'd be happy to answer your questions today.
Technically, if she contributes nothing to the household, she's a guest and you can ask her to leave at any time. However, if she's been there awhile, to protect yourself, the best course of action is to formally evict her. Otherwise, you run the risk that she will sue and that a judge will find that you and/or your son conferred rights upon her as a tenant. If she contributed anything at all - groceries, cooking, cleaning, child care, utility payments, that could seen as a form of "rent," which confers rights on her.
If there was an agreement that she would pay rent, and she's not paying, you can give her a three-day notice to vacate the premises. Tex. Prop. Code, Section 24.005
. The notice must be in writing, and should be hand-delivered to her. Otherwise, you can give her a 30-day notice that her tenancy is being terminated and that she must move. Section 91.001
. If she doesn't leave, you can then go to court and file suit to formally evict her.
If there is no custody order in place, you may want to be prepared for the possibility that she will take the child with her. I don't know if your son will want to file for temporary custody before serving her with the notice (or at least before the 30 days is up).