Horses learn by instant association and are generally wary of stuff they aren't familiar with. They can't think rationally, so they can't think 'this time mightn't be so bad because...', or 'last time was OK so it should always be', or such. They remember/associate the basic emotions/'thought pictures' to situations/things. Repetition & consistancy is what 'strengthens' the experiences into 'training'.
Here's the way I see what you've told us...
She's had only 2 possibly OK experiences at loading - the first time, she was put through a chute. No doubt she was scared, but had no alternative. But there was not pushing prodding, pulling on her halter at least & sounds like quite a different experience to later, so wouldn't necessarily be associated with the latter times. Second time, could have been that she'd learned to lead well, perhaps used to going into a barn or such, had developed some trust in you... so it just happened without conscious effort - great that happened. And even if she got nervous travelling, as the initial loading was good, she probably wouldn't strongly associate loading with *travelling*. But I wouldn't budget for that as a rule, and doing so only once will not convince her that 'trailering' generally speaking is a good thing. For her to confirm that & generalise, you need lots of repetition & consistency, that it is indeed OK/good.
So her next experience was one she was hesitant about because it was different. I imagine, rather than let her take her time, because you needed to be somewhere, she couldn't take her time, it was all a bit of a push, she wasn't reinforced for 'trying' enough and so she became more hesitant & worried about it. But sounds like this is only the first worried experience and she wasn't too upset about it, so shouldn't have made a huge problem, so long as subsequent 'lessons' were good & reinforced her confidence about it.
Then, for whatever reason you had to unload her enroute, she of course didn't want to go through that again, there is now fear associated, but you need to keep traveling, rushing, so she really got forced... and panicked & reactive. She felt like she had to fight for her life. Even though this was only the second bad experience, it was a very strong one - she was put in 'survival mode', needing to fight for herself against humans & ropes. That 'lesson' will stick big time I'm afraid. You can get her over it, but there will probably be a... niggle, for a long time, that she's a bit more hesitant or reactive, less trusting.
It sounds like there have been a few more 'tries' to get her into a trailer unsuccessfully. Don't know how much force was used, how 'intensive' and stressful the 'sessions' were, but that they resulted in same level of reactivity as earlier means, IME, she has been pushed way too far and each 'lesson' has further strengthened that fear/belief that she needs to fight, cannot trust...
I know people often put down the idea of 'humanising' our perceptions about animals. And rightly so on many levels, when we mistakenly attribute human thinking, morals, etc on an animal. But in some respects, such as emotional responses, I think it's helpful. For eg. if you were to put the above into human terms, you may better understand what's needed to get her through it. So here's a little story...
Say you were abducted by aliens(who's language & customs you couldn't understand). There were some scary times, forced onto their ship for eg, but for the most part, they seem reasonable. Then one day they tell you to get into a box. You hesitate because it looks dangerous, but they start pushing & prodding you. You don't think it's safe, but end up getting in, very relieved when you're allowed out. But then they want you to get straight back in & you are more concerned, more hesitant & they are getting angry & aggressive. Now, your nervousness combined with their frightening attitude makes you terrified, so you fight hard, but eventually they subdue you & force you in. Now I ask you, would you 'get over it' if they kept trying to force you into something you're now SURE is very dangerous? How could they go about convincing you(without verbal language) that it was indeed OK?
I know, not having your own trailer is difficult(been there), but I would have begged, borrowed or... hired a trailer at least a few times, for float loading practice, *before* you had to move her. And that's what I'd do now, tho it will likely take a lot more sessions now she's in that 'headspace'. Lots of short, easy sessions(maybe 10 or more 5 minute sessions over a day, say), in a low key, not rushed setup, where you can ask her just to go in & out... or even just up to it or one foot in - whatever she is up to, that she can do with minimal stress. With repetition, she will become comfortable and confident about it & you can ask a little more. Reward her & release the 'pressure' instantly - take her away or such - each time you have a 'win'. Also don't pull/push when she is 'trying', give her time to think, to assess.
If she does try to escape or pull back at whatever stage, realise you may be going too fast for her & slow down your approach a bit, but keep pressure on when she does this, not enough for her to feel too trapped & get upset - let her move & go with her or let the rope slide, but enough pressure to be a bit uncomfortable. Then the instant she quits resisting, you quit the pressure.