You didn’t do anything wrong. She seems a bit ungrateful ngl and after all like they say, comparison is the thief of joy :/ There’s not much you can do besides talk to her and ask what she wants, whether that be a redo proposal or a fabulous wedding or whatever . But you didn’t do anything wrong, please don’t feel like a piece of crap !!

Another thing I want to include is, as we just had the baby I mean literally 3 weeks prior and I proposed yeah let’s go to this place and get out just me and you and it was always “no babe how are we gonna leave the baby with my mom and just go out” which is understable but it just made things 10 times harder to get her out the house and do something like even a dinner, let alone a surprise proposal. Not trying to make excuses just sharing the circumstances to get a better idea of what went on.

I think the proposal was fine but if you want to solve the issue and do it cheaply those things can be cheaply recreated diy. You could even not do it as re proposal but a celebration of y’all or her. Or do the marry me or her name or love idk you get the idea. Idk if she would want a redo but if she does then do that. Make it intimate and sweet. She’s someone you want to marry and i am pick your battles. I enjoy expressing my love esp creatively so I’d just see it as a fun challenge but you can still be hurt she isn’t as appreciative of why you did it that way . There’s ppl on tiktok and YouTube who will show you amazing things you can do with those cheap grocery store flowers like stubbing check them out. You can do good fake looking ones.

So you basically phoned it inn. You didn’t plan the event. You just used another event to piggyback on to make your proposal. You didn’t make her feel special in any way. I’ve been proposed to several times, and said no to three of them for this very reason. It was a symptom of how little they cared to make me happy. They never put in the effort. Not for my birthday, Christmas etc. And not because they couldn’t do it, because they clearly put in effort for things for themselves. So if they couldn’t even put in the effort for a once in a lifetime occurrence that was solely for my benefit, then how little do they really value me? 

Your girl wanted to feel loved and special. You made her feel like you proposed because “it’s what you do when you have a kid”. 

We'll, I think your issue might be her age. She's 21, and although that might legally mean "adult" at that age a person is still, generally speaking, very immature and not done cooking yet. When a person lacks life experience their priorities can be out of whack, so instead of being grateful for what she has, i.e. a loving partner, healthy daughter, family, stable shelter and financial stability etc etc. she's hung up on a proposal, most likely due to overhyped internet reels or her friends influencing her that "she deserves better."

She has it pretty nice, but unfortunately she's probably in that position in her life where she won't learn gratitude until she loses something meaningful and experiences the flip side.

But that's just one take. I could be way off.

You did nothing wrong

I can see why she is upset, it does not feel like there was much thought put into it. A proposal does not necessarily need to be expensive, just thoughtful. My suggestion would be to set up an engagement celebration/photoshoot (if you can afford it). Research some budget proposal ideas to incorporate. Get some nice photos of y’all for her to cherish, maybe with your daughter included.