There seems to be a pretty good consensus here about setting boundaries, and I agree.
First of all, the most important - I would not leave her alone with your child ever. It is really unfortunate to have to go to that length, and I imagine with a dh in the military, it will be tempting over the years to do it, but given her abusive history, it will be worth it to know that you have not put him into a situation of risk. For a little one, the first instance of abuse could be life threatening. And even if it isn’t, and at any age, the first instance can be emotionally scarring. Your child never needs to experience that, even the first time. Once you’ve seen the first bruise, it is too late. Start looking into other suitable babysitters for the times when you need them - get connected with local moms groups, secular, through your church, etc… and set up your life as though she doesn’t live near by, so that she is not the person you have to turn to for babysitting help in a pinch.
Second, as Monicad pointed out, she has told you straight out that she will not respect your parental authority. Believe her. Most grandparents who undermine the parents authority don’t come out and say it so clearly, so you can be sure that she is going to do this. It may be difficult right now to imagine how bad this is, but poisoning a child against his parents, and teaching him not to respect his parents, can be downright dangerous, both physically and morally for a child.
Third, I would suggest that you end the discussions about names and birth plans. You may need to inform her, politely, but firmly, that you are going to go to the hospital with just your dh, and that you are not going to take any visitors (either at all, or until you are feeling up to them after the birth), and then do not get sucked into an argument about it. Just repeat that this is the way it is going to be, and if she continues to argue about it tell her that if she doesn’t respect your decision, that she is not going to be allowed to visit at all. If there is any possibility that she is going to show up anyway, do NOT call to tell her you are going into labor. And on your birth plan, at the very top, write that any visitors (or if you want to specify your mother) are to be turned away if they come to visit you. Then make sure to tell the staff in person also when you go in to give birth.
With the name, also refuse to argue about it. You can decide if you’re going to tell her the name ahead of time or after, but whichever time you do it, if she complains or utters a negative word about it, even once, tell her that it is not up for discussion and you are not going to argue about it. You will have to be willing to leave the room / hang up the phone / ask her to leave / etc. if she does not respect your statement that you are not going to discuss it.
With the clothes, you may need to tell her, “thanks, but I can’t take any more clothes right now, as I don’t have the room for them.” As another poster mentioned, you can even say that anything more you get will have to get donated, because you don’t have the room. You don’t even have to tell her you’re going to donate them, you can just do it.
The showers? I’d just let those go. Let them happen however the planners wish to make them happen, and don’t stress over that detail.
I think you’re going to have to gear up for some conflict. Unfortunately, there is no way around it, short of completely cutting her off. She is going to have to understand that if she wants a relationship with her grandson, it is going to be on your terms. She will have to respect your wishes, and your authority as the parents, and if she doesn’t, contact with the child will be limited, because your first priority is to raise your child as you see fit, and this will not be interfered with. She may need to be told this straight out. This is going to be one of those really difficult things that parenting demands of you - the good thing is that being responsible for another little soul forces us to do things that we otherwise would never have the guts to do. It makes us grow, which is good! The other good news is that because you are already being challenged, you are being given the opportunity to practice setting boundaries and being Mama Bear, BEFORE your child is in the middle of it and aware of the conflict.