I don't think you should get married just yet.
I think your fiancée has a point. Both of you had a dream wedding in mind (it wasn't just her), then your mum threw a strop, the rest of your family piled on, and you decided to change your plans because of that. It doesn't sound like the change was a mutual decision and it doesn't even sound as if this is what you want.
If both the bride and groom are unhappy with the wedding plans, there's something very, very wrong.
I understand your siblings saying they couldn't make it because they couldn't get childcare. You and your fiancée should have accepted that too. You don't say if you did. But there was no reason for your mum to throw her toys out of the pram (I'm assuming all of her kids are grown up from your posts) and she derailed everything.
You cannot start a marriage with your wife believing - because it's true - that you'll always take your mum's side first.
I'm not saying don't get married ever; I'm saying you have some things to work through first.
I would advise making some time to spend with your fiancée, owning that this wedding situation has got out of hand, and asking what you can both do now to rectify things, because she is your number one priority and you can't stand the idea of her being so unhappy about what is going to be a new chapter in your lives together. Ask her if there are any changes you can make to the wedding that are within budget, and agree that all decisions will be made jointly by the two of you and not anyone's family. Because you are each other's family now.
You were just kids when you got together, and I think for that reason, your mum hasn't quite realised you're not still her kid son holding hands with the girl down the road - you're a grown man, you're entitled to have your own wants and opinions, and you're hitching yourself to your chosen life partner, so she is going to have to back off a bit.
She might have been entitled to be overprotective in the very beginning, but we've moved on by maybe 15 years (depending on what exact details you fudged for anonymity - don't worry, we get changing a couple of bits for privacy). She has other children who have their own children, and she must have learnt how to dial things down a notch with them by now - it's your turn.
Your wife doesn't have to adore your family, but as you are seemingly close to them, she needs to get to a place where she can be civil with them before the wedding. I think it's fine to have that as a goal, as long as you acknowledge that a lot of these problems are down to you and your family - she's entitled to feel upset towards them, they didn't act well. But if everyone is committed to moving on, you need her to move on too. This has to come with the caveat that if they ever treat her badly again, you've learnt that you need to stand up for her first.
And make sure your family knows your priority is your wife (you're not the baby of the family anymore) and you won't tolerate shit towards her going forwards.
It's all a big mess, but this could be the making of your relationship if you can work through it properly.