To not ask the bride to approve my outfit for the wedding

That's batshit. Don't do it. 😬

Make the getting ready "special" for her? The woman that doesn't think highly enough of her friends to feed them dinner, expects you to sit on your arse in her house for the morning watching her get a face full of slap, have you and your DH drive two cars to the same event, then spend the afternoon kicking about, then be grateful to get to go to the evening bit. Why, just why have you agreed to this?
She wants champagne Instagram princess pictures on a Tesco own label budget.

Friend (male) arrived at our wedding looking like he'd been dragged through a hedge backwards. My husband and I did laugh about it. They'd come from Switzerland and we're going on an activity holiday afterwards so think things got a bit squashed. Just delighted they came to be honest. We were in our late 50s/early 60s and second time for both so these bridezilla things didn't bother us.

Act stupid and uninformed.
wear what you want. On her big day, shush her if she starts being negative.

”Aw this is your big day, don’t ruin your makeup with frowny face”😂

If this was my normally lovely friend, I would tell myself that she has gone raving mad, but temporarily, and will hopefully be sane again after the honeymoon, so I need to survive the next few weeks... And meanwhile, I would buy the dress I want and send her a photo saying I had to grab it without first getting her approval because it was on sale and I'm a bit broke at the moment, isn't the dress absolutely perfect, and how is everything else going?

Sounds like an attempt to get a couple of freebee bridesmaids. She sounds like an absolutely awful person for criticising peoples dress choice and size. I couldn’t be friends with her, personally, I guess all you can do is stand firm in your dress choice and distance yourself.

Are you in the UK? I’ve never heard of people not being invited to the ‘dinner’? Do you mean that you are going to the ceremony and then have to entertain yourselves for a bit before the party in the night? That’s really odd if so

It all sounds like you’re all making much more fuss than is needed. If you aren’t invited to the reception / dinner then I wouldn’t bother with your own professional hair and makeup only for sitting at the ceremony. Just do whatever you’d do for a night out or special occasion. Can grandparents not have DD for the whole day? If bride is having her own hair and makeup done professionally then what are you actually expected to do in the morning of her wedding? My friends all voluntarily came to the bridal suite on the morning of my wedding but it mostly consisted of us all drinking champagne in our bathrobes, it wasn’t a chore which any of them asked to be thanked for.

This. Have some self regard. Don't do it.

The person who voted YABU must be the bride 🤣👌🏼

A bit bridezilla? That's an understatement.

Why are you even friends with someone who is rude about people's weight/size and so bossy and demanding? Is she always so delightful?

No sympathy for any of you.

You can only be a doormat if you're happy to lie down and allow people to wipe their feet on you.

Which you're all happily doing, so you'll have to suck it up 🤷‍♂️

Where does this behaviour come from? What makes ordinary people think they're royalty (whom I loathe) for this incredibly ordinary thing? "Princess for the day". Why? Of course it's a very special day for the B&G and their loved ones, but what kind of madness takes hold in these people?

Anyhoo. I agree with the pp's, you've got to talk with your friend.

Either talk to her and ask her to dial things down a bit - say you're concerned as she isn't acting like herself. OR step back - quietly and graciously let her know you can't be there on the morning unfortunately, invent a plausible excuse. If she asks what you're wearing just say don't worry, it will be lovely. And then bat back any other questions and change to topic to whatever is going on in your life so she might realise that for the rest of you her wedding is not the absolute centre of your lives.

Bin that off, mate.
Save yourself some time, money and effort. Don't go.

This is easily solved. Don't go.

She is batshit and needs a reality check, and you as a friend can be the one to deliver it. Surely building up all this resentment of her behaviour won't make for a lovely wedding and reception if you're all seething at her over the steamed salmon?

If it’s not her usual behaviour and you actually like each other then why on earth don’t you say something? There’s no point just seething and getting resentful about the arrangements and costs and ending up with the friendship spoiled that way.

“Kate, I understand that wedding planning can be stressful and you want the day to be perfect, but you are being a knob about a lot of things and it’s making things stressful for me and no doubt many other guests. We can’t come and help you get ready in the morning if you aren’t going to include us in the hair and makeup session because we need time to get ready ourselves.”