If it's weed and she never does it around her son, or cares for her son stoned, then no, I don't see it as a reason to lose your child at all.
I also don't think Barbara is that great for him either. She constantly instigates argument with Jannelle while Jace is there, awake! Name calling, yelling, etc. Even before she has custody she purposefully did the opposite of what Janelle wanted. Changed him when she dressed him, tried to lure the baby away from Jannelle when she was holding him, etc, etc. No one is saying she perfect, no one is saying she's being at all a good mother.. I just don't think the alternative is really all that much better at all.
I agree! I think Jenelle has a lot of growing up to do, but i think her mom is nuts! Even if her daughter was a "good" mother. She has a few screws loose up there.