Call girl, you say they were "dating for 3 years" , not girlfriend and boyfriend, just dating...
I don't think he had any intentions, ever of making anything serious and he possibly even told her so... Maybe, she got pregnant deliberately, he's all she knows, she's soft spoken, probably thinks he's all she deserves. I have no doubt that a man like this, controlling will be so behind closed doors, until he is married, then it's his business in his eyes.
There is nothing you can do other than be there for her and try to bring out her personality, allowing her to see her own self worth, commend her constantly over how good she is being a Mother, how good she looks anything so her esteme rises above his.
What ever he put her through, through pregnancy stressed her to the hilt, she's still stressed... Be there.