MIL has to learn to be hands-off.
You need to remember, YOU are the Mommy.
"Disciplining" a 6 month old is, not appropriate. But re-direction and distraction is age appropriate.
Read this link:
http://www.google.com/search?hl=en&client=firefox-a&a...
THEN, print it and SHOW IT TO HER.
As you said, your child is just a BABY. Babies cry, they scream, they whine, they are babies. They CANNOT talk yet...thus, this is their only way to communicate. Well, I"m sure you know that already, obviously.
My Mother was like that in the beginning... and I am a very different parent than she is. It doesn't matter whether or not a baby "understands" the word "no." But it does matter, that BABIES DO NOT HAVE IMPULSE CONTROL YET. "FULL IMPULSE CONTROL" DOES NOT HAPPEN UNTIL ABOUT 2-3 YEARS OLD.
Your MIL cannot expect her Grandchild to be perfect. And besides, always telling a baby "no" without letting them explore....will just teach them that they can't do anything correctly.
Babies learn by exploring and making messes, and making noise, and by trial and error.
I would recommend getting a book on baby development. A good one is "What To Expect The First Year" by Arlene Eisenberg.
Sorry to be so emphatic...I'm not criticizing you, but just the MIL ideas that a "baby" has to be disciplined.
With my Mom and MIL... well, me & Hubby stood our ground TOGETHER... and told them in many ways that "we are the Parents, thank you, we have our own ways. This is our first child...let us enjoy it. If you want to "discipline" our child...you need to first come to us...it will be up to us on what to do." We just kept repeating this and reinforced this....and eventually they got it. Your Hubby also needs to support you in this. This is your child, not your MIL's.
Yes, it is so irritating. I put up with that for years. It took time for my Mom and MIL to concede. My family is very overbearing. But, it can work out. You just have to stay consistent in replying to them.
You are doing fine... you are the Mommy, and each Mommy has their own way of raising their baby. This is your first child...enjoy that. Remind your MIL, that this is your special time to be a Parent, she was already a Parent...so let you enjoy yours.
All the best,
~Susan