Honestly I don't know.
You would think second hand meth
smoke would not be so bad, compared to lets say second hand cigarette smoke or marijuana
smoke. The reason being Meth smoke is not actually smoke, its vapor. Vapor doesn't stay in the air near as long as smoke, it dissipates quickly in the surrounding air its much different than regular smoke you are used to.
On the other hand, a trailer is a very small space, 7 years is a long time considering it was pretty much 100% of the baby's life, also she was an infant/little kid, it might not take much at those ages to effect her brain permanently.
I know you are just trying to do something good cause you care about her, and maybe this is the only thing you can do, but asking such a question on a forum probably isn't the best idea if you really want an answer. Have your mom take her to a doctor, have a brain scan done or something. Asking a bunch of strangers on a forum who are mostly ex/current tweekers and speed freaks isn't the best idea, not to say there isn't A LOT of brilliant people on this forum. Good luck, i hope the little girls ok.