I would keep the trailer you got and work on training the mare...

Too bad you're not closer.  I'm looking to buy a 2H slant to replace my 2H straight load with back ramp.  My mare doesn't haul well in a straight load.  Steps all over herself. She rides fine in a slant.   Go figure.

I am personally looking for a new horse trailer myself, and their are so many to choose from that it can get your head spinning.  However, a good friend of mine has a 4H trailer.  Since I've been looking myself, I know they offer many different options in the horse area, such as the 1+2, side ramps, straight loads front to back.  This brand went out for a while, but her trailer is probably over 20 years old, and still in great condition, and the usual "aluminum dust" that comes off on your hands like with sundowners and most manufacturers, has not occurred yet.  This is something she complains about other trailers a lot which is something I would not have noticed, but lends to the quality of the product.  As with any trailer co, you can have them add ramps or step up.  I can attest that we have loaded too many to count onto her 4H and never had a single problem a refusal.  Even first timers.  I can appreciate the feeling of being in close quarters in the trailer.  I have a good loader, with the exception of 1 trailer, and I'm sorry, but every horse that has been on the trailer, and then attempted to be re-loaded, will never get back on that trailer which is an Adams.  My horse who is my personal therapy horse, that we trained from baby who never had a problem, the guy with the Adams did the whole load on the trailer yourself thing because I too have problems with the enclosed area because I'm physically challenged after an accident with a horse in '97.  Have you given thought to a stock area trailer.  I had a horse that went on the trailer great the first time(straight load, 20 some yrs ago) that when they closed the door where he could see me on the opposite side from the driver side where he was loaded, decided he didn't like that someone was separating us, and he came over the chest bar (solid back then) and was teetering.  Some guy picked me up off the ground from freaking out at 19, and my first horse I personally trained, and was still only 2yrs old, as glass was breaking from the windows all around me, dragged me to the back and said talk to your horse.  Once he seen me behind him, he got himself off the chest bar, and rammed the back ramp to break the pins and down came the ramp, where he flew off and spun around and put his bloody head around my neck, and pushed out a big breath.  At least he was off the bar.  The problem was, we still had to move him.  The answer was a stock trailer.  That's what we have now and even though we are looking for another trailer, we will not trade the stock in for another.  We use it for so much, and for horses that have similar problems as yours.  It was a life saver.  I know they even make LQ/tack area trailers with stock in the rear.  They have come a long way too.  The open area is generally higher up, with no open area on the bottom, so that your horse isn't as exposed as before, but for horses that are clostraphobic which is what sounds like may be your horses issue, since she gets sweaty in the trailer.  Indicates that she is getting herself worked up before she even gets to the show.  This must be difficult for you, as your horse has wasted so much energy on the way to the show, that she can't be at her top form in the ring.  Any way you decide to go, best of luck, and most of all safe travels, with awesome shows and adventures.  Sorry for the long message, and I really hope that you found something helpful in this forever long note.