It's not you.
I also have a daughter who can happily undo the pushchair straps and slide out the front so that I would run her over if I didn't stop.
Or fling herself sideways so far that her head could crack onto the pavement or she tips the pushchair over sideways.
Unfortunately she is also an expert car seat escapert too - she will graze, bruise and hurt herself wriggling arms out of tight straps.
Some children hate being constrained so much, and have such anxiety about being forced that it really isn't an option.
I do think there is something to be said for alternative pushchair designs - try something with a deep seat, sat low to the floor and 5 point straps.
Other things that help:
We take the toy pushchair out and she pushes Teddy or dolly. Okay for relatively short distances.
Keep the pushchair facing me so so we can chat and sing
Offer snacks amd drinks when they are in (this is sort of bribery, but it's more about distraction and ensuring mine feels cared for, comfortable and remembered once in - she needs to feel that her needs are still met even when constrained)
Check they don't need the toilet. Mine wouldn't go in with a wet nappy or if she needed a wee, and now potty trained, won't go in or walk if she needs to go.
Favourite Teddy strapped inwith her.
Make sure they aren't getting too cold, too hot,or blinded by the sun in there. Again, it's the being trapped while uncomfortable that seems to create the anxiety for mine.
I've also have lots of conversations about being a big girl, too heavy for mummy to carry (hopefully haven't created and eating disorder etc). I now never ever carry her unless the situation is dangerous. (E.g. she is being silly in the middle of crossing the road)