MIL problems since having baby - AIBU?

Speaking as someone who's put up with years of this type of bullshit I'd advise to grow a backbone now, otherwise you might be in for years of stress and resentment.

I wish I'd spoke out earlier because my relationship with my in laws is damaged beyond repair.

She is taking advantage of your nature to feed her desire for power and control. As scary as it might seem you’re going to have to set strong boundaries now. For example
“Don’t take her out of her car seat please she’s happy in there, I’ll get her out when she’s ready”.
”If you’re leaving the room I’ll take the baby, I like to keep her close to me given how little she is”.
“No kissing on the lips, it’s not safe”.
“Do you mean to be so rude by talking about my appearance?”.
Any sign she’s not respecting your boundaries and you must say
“We’re off now. Bye”. No explanation, no bargaining, just a clear communication through action that her not respecting your boundaries equals her not getting to see you all. After a few times she’ll get a clear message that she has to behave herself. If you don’t see these boundaries now I’m afraid to say you’re destined for a life of stress and anxiety. Good luck.

Why would you just stand their like a limp lettuce whilst she prizes YOUR baby out of your arms or pram and takes her away?

Unless you find your backbone then this will continue.

She sounds very difficult, but you will make life easier for yourself in the long run by being calmly assertive now. My MIL used to make comments about how I did things, especially breastfeeding. At first I just hid away for feeds and felt anxious. Things improved when I started standing my ground.

You don’t have to do it in an argumentative way, just firmly: it’s time for their nap now, and take baby back.

If she criticises, you could start with the Mumsnet standard: did you mean to be so rude?

YABU - your mil is excited and wants to be hands on. She has no idea she’s upsetting you or that you’d like her to act differently. You’re not engaging with her at all. You’re not speaking up.

You are the mother and you need to lead the situation and jump in sooner.

“Hi MIL, baby’s sleeping in her car seat and she really needs it, so we’ll pop her down here for the moment whilst we have a quiet cup of tea”

”wait up MiL I need to burp her first, or shall I show you how she prefers it”

”no need to wander off with her, let’s sit down in the sitting room”

”baby is so comfortable with me right now, I don’t want to disturb her, I’ll let you have a cuddle in a bit”

My MIL and my own mother have been weird since I had babies. I think there is some jealousy / competition there. It's really sad and annoying, especially when you just need some support.
My MiL was always interfering and trying to show me 'how it's done', my own mum was weird and got really defensive and angry whenever I did something differently to how she would have done it.
Exhausting really. I'd look at friends who's mums really were genuinely helpful and caring and and feel really put out.
Set up some boundaries. You are well within your rights to be sensitive - it's not you who should change it's them.

You tell her NO. Baby is staying with ME. Any rude remarks, you icily say “I beg your pardon?” I’m afraid you have made a rod for your own back being so passive this far, put your foot down before it goes further. You’re in charge of your own child.

I know it’s easier said than done but you really just need to say no and stick up for yourself x

To be fair, if you have bitten your tongue for years, your MIL may not realise she's upsetting you.

Today is the day you say NO!, thank you. Tell her bluntly that you are feeling uncomfortable, that having your child removed is not on, and it won't be happening in future. Or follow her into the other room and take YOUR baby back.

Buy a sling and put baby in it so she physically can't interfere.

If she continues with her behaviour, stop going to see your MIL. When she undermines you, pick up your baby & leave. Block her on your phone. Keep your doors locked.

You are an adult. You are your baby's protector. Time to make a stand.

She's obviously being massively unreasonable but I don't really understand how she's taking the baby literally from your arms. My response would be "what are you doing?", and just not letting go if someone just walked over and tried to take my baby.

Stop visiting her. Invite her to yours less.

What does your partner say when she insults you?

You say you have never had any issues before, but had years of biting your tongue. Now is the time to speak out.

How often do you visit?

I could have written your post myself.

It took 6 months for my partner to have a word with her about her behaviour. It was way too little too late and I can't forgive how she acted. I've never had any sort of acknowledgement or apology from her.

I'm now overdue with my second and I don't want her anywhere near me.

I won't stop her having a relationship with my children but I have no involvement in facilitating that and use time when she visits as time for myself.

Everyone is too scared to call out her bad behaviour and tiptoes around her. Once I decided to stop bothering with her my anxiety got better. I have no desire to see her at this late stage of pregnancy, it isn't worth the stress.

Good luck. Sadly not an uncommon experience.

I've voted YABU because you're sitting back and letting it happen. She's your baby and you need to speak up for her.

Stop going to see her. If she wants to see the baby she waits to be invited to yours and then you call all the shots. Tell your partner to grow a spine and to ensure she treats you with some respect and consideration. Or I would be telling her to fuck off frankly.

You need to start standing up for yourself (and your baby). It might be hard in the beginning if you are not used to it but you have to learn it yourself take care of your baby. And tell your DH he needs to stand up for you three and tell his mom to back off when she keeps crossing the line.

You simply need to say no.
When she reaches for baby - 'she is staying here for now'

when she goes to pick her from pram /car seat asleep - 'she is sleeping there right now, please leave her'

when she's going into another room - 'can you please stay in here mil together'

You need to say no...