Thank you for all the advice. If I come off uncaring or whatever it's not how I am (really I am one of those super neurotic worriers), I have put a lot into this horse and really adore it more than any other, that's why I just want to be able to do something with her. And I am just tired of it all, it's not just this but other injuries she's had, troubles (unrelated). And I had such high hopes for this horse.
I had the vet out they didn't really have a clue, but that it didn't seem joint related and that she wasn't in pain and recommended someone to work on her back and just time off (not that she had been working). He said I could get further tests but I would end up spending more than the horse was worth and he didn't really think they would help. I had multiple sessions with a very reputable and trained equine back person and she said that, from her opinion horse wasn't in pain and I should bring her back into work, and it was her thought that work would improve this issue, and just sort of evaluate as I go along.
She's not suitable at the moment to be sold as a child's mount or a trail horse, and I am not considering selling her, if I decide that she shouldn't be ridden I plan to just keep her as a pet or something, but it would be nice to keep her as a trail horse for friends later on, and if I have kids in a few years she could be a lead line horse, or even for my little cousins.
As I said, she's seven, hasn't really been ridden properly for three (or more) years, so of course I'm going to get on her in an arena before heading out on a trail, considering it's a possibility she's never even been on a trail/road. Like it's great if other people have the confidence to take a horse like that out on trails and roads alone, but I certainly don't! Her steering and stopping needs major work and I'm not going to work out that out and about. I've been getting on her for about 10-15 minutes at a time and just working on steering and stopping, first in an enclosed arena type area, and then a paddock. I saw no signs of discomfort and she seemed to somewhat enjoy getting out and about. The other day I asked her to trot and she was really reluctant and once she did was near impossible to keep straight and kept ducking to side, rushing and then dropping back to the walk. I sort of try to bring her around in a circle (or square, not asking for anything like flexion or even contact but a manageable space) and she'll just cut right in, like she'd want to do tiny circles. I haven't ridden her since then, some people are saying to stop being silly and ride, but I don't know, which is why i posted here.
But it's probably best if I try and find some people I can get good advice from in person, as it's quite a strange lameness, and she's quite a different little horse and it's hard to give and get advice online. I'll probably give her some time off and re-evaluate again later on. It's just tricky to know with her because she is the kind of horse who will try and "get one over you" whenever she can. It is just such a shame to fully retire a seven year old lovely horse.
Sorry for the long post, thanks again for replies