My child is 12 yrs old and I'm wanting to know can she make a legal decision about going for visitation with her mother? If so do I need to go back to court and get this in writing in another court order?

No the child can not made any decision. The custodial parent will have to go back to court.
But unless there is a real reason that the other parent is a danger, I dobut they will stop his visit rights.

This is a hard one. Legally the chold cannot make a decision here. That part is legal fact. If you refuse to allow the visitation, you can be cited for contempt of court. But, from a practical matter its hard to force a child to spend time with someone.

So, what you do is go back to court and ask for a modifciation of the child custody order.

If you don't want to force the child to go see her mother then go back to court to ask for a modification. Both answers are correct in that the child can not make a legal decision and if you do not do either option then you can be held in contempt (which yes can result in jail time, usually getting a warning first). Keep in mind that if there is no reason the judge can find for discontinuing or lessening the visits the order may not be modified.