Welcome to JustAnswer.
I agree with you that it should be a crime. In a few states such as South Carolina and Tennessee it is a crime, but not in Louisiana.
Louisiana does have a couple of state statutes on the subject, but none that make it a crime. One statute provides for the creation of multi-disciplinary teams to deal with the issue of when a pregnant woman arrested for something else tests positive for drugs. (See link below.) That statute provides that the pregnant woman may be committed to a treatment facility until her criminal
case ends. Again, this only applies if the woman is arrested for a crime. She, unfortunately, cannot be arrested for using drugs while pregnant.
Another LA statute directs the Department of Health and Hospitals to provide drug treatment programs to pregnant women. (See link below.) One interesting thing about that statute is it says, "This state, therefore, adopts as the preferred methods, prevention, intervention, and treatment alternatives rather than punitive actions to ameliorate the problems related to such medical and social risk factors."
Basically, this means the Louisiana Legislature has chosen to try to promote treatment of drug addicted pregnant women rather than criminalizing it. The argument being that criminalizing it would make pregnant women less likely to seek treatment. I don't agree with this stance because most prosecutors are reasonable people whose goal would be to protect the unborn child rather than imprison the mother and having the threat of criminal prosecution would make that easier to accomplish.
Sorry I didn't have better news for you. That was incredibly selfish and irresponsible on her part.