I contemplated AIBU but chickened out! This is long, sorry, but I would really appreciate any thoughts about what you would do in my situation. Hormones are probably not helping me at present...
I have a difficult relationship with my DM. Not a great childhood and don't speak to my DF. I always felt like DM preferred my brothers growing up. DM gets quite lonely and is unsocial. Doesn't really have many friends as she makes excuses not to go out. I find her quite overbearing at times, like I am being smothered. It's the complete opposite to when I was growing up and it just makes me uncomfortable. She has recently made a big decision and told my brothers and aunt and uncle, but didn't tell me, I found out via my uncle. When I spoke to her, DM declared that she had told me and I must have forgotten which is rubbish, she knew I would say I don't think it's a good idea and she deliberately hid it from me. No one thinks it's a good decision but it impacts me more than anybody else. DM has history for making snap (and poor) decisions and will do her best to avoid discussing them. Then, in hindsight, says she wishes she had listened to us.
Anyway, I said I needed a break as I need to focus on myself and the baby at the moment, and left the family chat group. DM can be quite emotionally manipulative and I think is depressed, but she isn't proactive to change anything if it requires serious effort, hence snap (and sometimes irrational) decisions. It's like she is lost and looking for a purpose in life. She has been asking for a grandchild for 5+ years. When we ask what she wants for her birthday, that's what she says. It really irritates me because she isn't joking, she is serious.
Coming back to now...I am due to have a c section in the next couple of weeks. My brothers say DM is acting normally and hasn't brought any of it up with them. They don't think there is a problem with what I've said/done, and support me in terms of holding out because DM just doesn't seem to see the problem.I am REALLY enjoying the freedom of not speaking to her. I feel liberated. No phone calls at random times with messages of 'I only wanted a quick chat, but you must be busy....' to respond to. No random family chat messages that I feel I should reply to in order to be polite/not get individual messages chasing me up.
I don't think I want to speak to her before I have the baby, or even immediately after to be honest. And this is where I get stuck. Deep down, I feel as though she will get in touch because she will want to know about the baby. But it makes me feel kind of used? If she gets in touch at any point between now and the baby being born, I genuinely think it will be on the basis that she wants to sweep everything under the carpet and not miss out on her first GC. I don't want to be spiteful, but I feel quite upset at how she's behaved recently (she also upset me a couple of months ago). I feel like I'm a vessel to fulfil her desire to be a grandparent 
Am I massively overreacting? What would you do? I can give details of the disagreement etc but this post was in danger of being soooooooo long that I didn't go into the detail. I don't think my DM is on here, I'd feel appalling if she saw this because it would probably crush her, but I am so emotionally exhausted. I feel as though I am her parent most of the time...