Well being a new mom sometimes you have to learn from people telling you or from your own mishaps. I would try suggesting things to help her out. If you are really concerned I would speak with you son about whats going on. You will able to confide in him with out starting problems.

When a Mother leaves her child and comes back and she is OUT OF IT SHE WAS HIGH!

SHE WENT OUT AND GOT HIGH!  TRUST YOUR GUT MY FRIEND. THIS IS NOTIME TO BE PASSIVE YOUR GRANDCHILDS LIFE IS AT STAKE AND YOU MUST SPEAK UP! TODAY

If you babysat and she went out.... usually time away from a baby REJUVINATES A PERSON.

If this is her first child than you need to train her in a very loving but firm way FOR REAL

Make her quite aware If your dropping the baby off at 12 noon and your picking her up at 6 pm

 I want 3 changes of clothes just in case,  I want at least 15 diapers dont worry you can leave some here or take them with you, and Three prepared bottles and baby wipes. 

You are instructing her,  setting boundries and when the baby first came its all nicey nicey you dont want to hurt feelings etc screw that.  She doesnt work....she sounds like she doesnt appreciate you,  or respect you coming in late not enough diapers.

Now your taking time out of your day which I know you love that baby but without being firm this daughter in law will walk all over you the REST of your life.  Also say to her if you come back the way you did and I dont care what you do when your away from this baby dont bother coming back til you go sleep it off becuse whatever you did I know you did something and I WONT ALLOW YOU TO PUT MY GRANDAUGHTERS LIFE IN YOUR HANDS AND KILL HER IN THAT CAR BECAUSE you needed to go get high!

Honestly, unless you TRULY expect drug abuse, I would mind my own business.  Not all mothers are the same and you have no idea how she is when you are not there.

If you see some sign of abuse toward the child or that she is abusing herself with drugs or alcohol, then you should do what you can to help.. to protect the baby.   maybe start  by talking to your son.. otherwise....

My sister in law sounds just like your daughter in law.   and my mother inlaw constantly has something negative to say about her parenting!   But, when we are at my sister in law's house.. when she is with the kids.. she's a great mom and the kids are great.    yup.. she is lazy.. she forgets to bring enough diapers.. she's a flighty one.. but, all in all, at the end of the day.. she loves her kids, does the best SHE can, and is a great mom.. and it shows in the kids (now ages 3 and 5).     but her meddling.. negative comments and suggestions have left my sis in law hating my mother in law.  

thanks to everyone who gave me a comment/advice, i appreciate it.  and no worries.........i don't meddle.  i have NEVER butted in.  was just concerned for the babies well being.  thank you,  dee

That's good dea.  I wouldl hate to see a riff between you and your son or something like that.   ;-)   You seem like a great grandmother.  :)