I am sorry if this sounds blunt, but I think you should put your feelings and the babies feeling before her. She has had her chances.
If you keep the baby, she might feel bad.
If she gets the baby, she might go on drugs again, the baby might be hurt or worse, and you would really, really hurt. In fact, you might never forgive yourself for letting the baby go back.
What makes me really, really mad and sad. about this, that there are so many women the world over, myself included, desperate to have their own baby. Yet people like this can be blessed with a child. However, if I tried to adopt an addict baby, I would probably be out through months and social security checks, and then turned down because I am too old. It is so not fair.
Do what you feel safe with. Could you also get more support from other family members so that this can be discussed and a united front put on that voices the same opinion. It seems unfair you have to deal with this and she may get very manipulative.
Good luck
B
x