@Areyoufree
It's always been a frustration of mine, partly because I love to walk, and partly because every other bugger seems to have kids that love to run around. My nephew was walking up to 6 miles a day when he was two, so it's always been hard not to think that there is something I am doing wrong! To be fair, I think my daughter struggles with being around lots of noise and people, and this is why she gets upset. I find the additional needs thing tricky, because nothing is black and white - kids can struggle or tire easily without reaching any diagnostic criteria for SN (although, have no idea about my daughter, as it is impossible to get a referral in my area). I think that's why I try not to have an opinion about these things, because every situation is different, and most people are just trying to make things work!
Genuinely, in almost all families I know, if the parents are keen walkers - even more so if they don't drive - then the kids also walk long distances without complaining. The kids I know who moan and whine and refuse to walk are generally the ones who are driven everywhere.
That's why I was surprised, given that you sound (the same as me) someone who doesn't drive and loves to walk everywhere, to hear about the difficulties you're having with your daughter.
I do think that it might be worth getting some sort of investigation done (though I don't have any expertise about what it might be, but you've had some good suggestions here already I think) because it obviously isn't something you're doing wrong.
Like I said, I don't pass judgement on people I see out and about (unless they're stuffing their kids with Haribo, hitting them, or smoking in their faces) but on a thread like this (which explicitly asked for others' thoughts) I think it's reasonable to offer a view.
I hope things improve with your daughter soon. 