FGS people are jumping to ridiculous conclusions about this young woman.
If a 19 year old is selfish and self centred having a baby will not turn them into a selfless grown up overnight.
She is the same 19 year old she was before she had that baby.
She needs to learn how to be an adult and a mother. It doesn't come naturally to everyone. There are plenty of older women who don't take to it right away and no one tells them to hand their baby over to SS.
The OP is doing an amazing job but its true that her DD is unlikely to step up if she doesn't have to.
She sees her mum as someone who is there to sort everything out.
She is untested as a mother. She needs to be tested before anyone starts flinging about 'shit mother' labels.
Withdraw OP. Stop getting up to settle your GD, stop doing the mum stuff.
You are on hand to make sure she isn't neglected.
IF your DD is unable or unwilling to do what she needs to do when you are NOT doing it, you will need to have the tough conversations.
This cannot go on forever with DD being a Disney mommy and you doing the tough stuff.
You will know best what approach to this will suit your family.
Withdraw bit by bit until DD is doing the bulk of the work or sit her down and tell her exactly what is expected of her.
She needs to tell you WHY she isn't parenting her DD. No fecking about. Is she scared? Does she feel you have pushed her aside (not saying you have)?, is she overwhelmed?, has she bonded?
No need for ultimatums but she needs to know the possible consequences e.g. losing care of her child to you and all that entails.
Good luck