The casting
The overall casting has been very good except for 1 .
Deb,
The acting is ok but the physical difference is to big to ignore.
Deb is tall and skinny, the new one is short and boarding on chubby.
But its explainable because teens have baby fat, and a lot of people have looked chubby or moderately chubby and then become thin during their 20s. I've seen it a lot, so I trust this casting.
As for her height, Jennifer Carpenter is 5'9", while Molly Brown is 5'3", so you may have something there, but I'm not sure if they'd find a taller actress who can nail this role the way Molly Brown has. They might have, but I can't be sure.
Plus it is possible for a female to gain a couple of inches in their late teens, so you can at least explain some of that height difference. Plus on-screen its not always clear how tall they are.