From what you say in your post, your main concern is that you fear not being in control. This is common in new Mums which I presume is the case and with your first child.
One thing that we all have to learn is not to take offers of help or others opinions to be criticism, they are so often not.
You can shut out other peoples views by simply shutting the door and not hearing them, but they will still hold those opinions and views of you, and they may not be negative views, as it seems you think in this case they are.
I also found your Husbands insensitivity astounding. What was to be gained from adding yet more fuel to your already well developed animosity towards your MIL, nothing. He may be part of the problem not the solution.
For what it is worth you have rejected the help of a person who so clearly want's to be of help, someone who will love and care for your child because it is their flesh and blood, in favour of strangers who are looking after lots of other children and babies who have no loving connection and are doing it for money. If as I think you might be a controlling person, then doing this you relinquish any control of how your child is treated in nursery. I am sure they will be cared for within the law and health and safety, but how can that compensate for one to one care in your childs own environment with a loving GM? So this leads me to believe that all this is about more than control. I suspect that you feel inadequate and that is making you worry that your ML might do a better job than you. Now if that is the case, no one can take the place of Mum.
If you can see your ML as a loving supporter, of someone who if you ask her to will conform with how you want your child to be brought up, with the odd slip, because that's what Grandparent's do...all normal, then you will give the best to your child, you will feel better about yourself.
I suspect you might not be feeling that good about things right now, and let's face it even your Husband might stop putting a barrier between you and his Mum once he see's that you value her views. You don't have to accept them, but be honest with her and develop a relationship that will benefit your family. It is always easier not to see or talk to people you disagree with or you feel are a threat in some way. But when you are family, it is always better to make good relationships, as far as possible. Don't bring up your child in a family that is disfunctional. You don't want your child in later life to build a dysfunctional family do you? This is what could happen if you set the wrong example now.
There is a lot hinges on how you behave now. Sit down quietly, having read all the good advice and views of you in all these responses on this thread and think about what you are feeling and really analyse those feelings and identify what they are.
I wish you well. You sound very alone and you think that is a good I suspect, because no one disagree's or challenges when you isolate yourself. The downside of alone, is that no one supports, loves or cares. These are your choices. I hope you make the right decisions. Choose happy, not sad, choose love not hate, choose tolerance not intolerance and you will be so much happier.
Best wishes.