For not allowing mother to birth of baby

As everyone else has said, this is a worrying level of weirdness and intention to trample all over your wishes. If I were you I’d warn the staff on your ward that she’s threatening to wait outside theatre when you have asked her not to. Otherwise she might cheerfully tell them you’re expecting her and they would believe her.

Your mother needs to understand that this isn’t about her… it’s a huge day for you and your DP as you get to meet your baby!

Sounds like you’re being reasonable and want grandparents to meet baby soon but would like a bit of space during delivery. She needs to respect that and as a PP alludes to, start as you mean to go on as this will be the very first of many similar hurdles and you need to prioritise your new family unit now.

Talk to the hospital staff and specify you don't want her around until you give permission.

Is your mum a midwife?? Because they are trained that mums can deny access to any visitors they want, including the dad.

Not only is she being really unreasonable to you, but I'd be concerned she isn't doing the right thing by her patients on this particular issue - is she granting access to the postnatal ward to grandparents of new babies because she thinks they have "rights"?

I would be very concerned that she thinks her job gives her “special privileges.” Exactly how far does she think that extends? Will she try to look at medical records? Will she cross the line while you’re in hospital? I think that perhaps it would be best if you notified the hospital that, in the name of family harmony, you just want to make sure that your MIL is not involved in your case and has no access to your files. And do state something like that, such as that it’s about family harmony or something, because I understand that you may not want to endanger her job. But you have the right to absolute privacy and your baby has the right for their medical information to be kept private as well. She is not entitled to any of this; as many have pointed out, there are no “grandparents’ rights.”

She’s being insane.

Be very firm.

Too late to switch hospitals?!

If she turns up without your permission, your partner will have to hold firm your boundary.

Easier said than done, I'm sure. But I have a feeling this won't be the last time you and your partner will have to stick up for yourselves, so I'd start as you mean to go on if I were you.

Wow YANBU, how is she not embarrassed by her behaviour?!

If be looking at going to a different hospital to give birth

I think you need to explain your wishes and feelings. This is the start of prioritising your relationship with your baby and immediate family over your mother.

You are not being unreasonable at all. My parents wanted to visit me in hospital after my c section. I said no, that was the end of it.

They asked to visit the day I got home with the baby (day after birth) I again said no because I was in no state for guests, that was the end of it.

Your mum is being extremely weird, unreasonable and controlling.

Your birthing experience, your choice. At first I said my mum could come in with us for our DS but then I changed my mind as my DH had the right his experience of being a dad and seeing baby for the first time, and not worrying about letting his emotions go infront of my mum (although they were very close)

She came to the hospital after I invited her, I don't doubt for one second she sat outside in the car park after she knew I was in labour until she got the txt though 🤣.
She did come very soon after though maybe 40 mins. But it's completely your choice .

Ah fuck, buckle up, the journey of batshittery has just started

Your baby, your birth, your choice.

I'd personally be very happy for my mum to be waiting outside and it would give me comfort. I genuinely love sharing the joy of a newborn with all of the grandparents and wanted them to come visit as soon as possible.
But that's me.
If you've told your mum how you feel, she should absolutely respect this.

I found my mum to be an absolutely invaluable support when I gave birth, couldn't imagine doing it without her tbh. But if I'd have not wanted here there then she'd have been absolutely fine with that - and even if she was upset, she'd certainly know better than to try and pressure me into it!

In any case, the sort of grandparent who is bringing up fictitious "grandparent rights" and trying to play competitive grandmas with your MIL for a baby who has not yet been born far exceeds the batshittery threshold to warrant being kept very much at arm's length.

There’s no such thing legally as grandparents’ rights. YANBU. She sounds like she’s going to be a massive pain in the arse about this.

She has zero rights.
But I would be very concerned about the level of batshittery a person must posses to come out with all that shit.
I'd be vary wary of what's going to happen there.