Legal Question in Family Law in Texas

You need to talk to a TX family law attorney before doing anything.

However, if you modify custody (1) the bio dad will need to be notified and (2) once it's done it's permanent. Therefore, if they don't want to return her later, you can't get her back automatically!

So I highly recommend that you talk to an attorney before proceeding.

For example, In the State of Texas, once a person has care & control of a child for more than 6 months, they have legal standing to ask a court to grant them custody of the child. I don't know what other states do in other jurisdictions. So if your parents take this child and keep her, they can seek custody & you can't get her back later if you decide that you want her back!