Length sounds short to me. If she is already wearing an 84" blanket, that means body is 7ft. She may really fill out that blanket length, or have some bit of extra fabric.
We have large horses, who also wear 84" blankets. They stand between 17H and 16.2H, girth at about 84", full bodied, not draft horses. They have 8ft length stalls, with butt bars about 4inches from the center door in the stock trailer. Stall divider is about 3inches wide, with inside trailer width of 6ft. No wheel wells inside the walls. So stalls are almost 34 inches wide. They travel well in these stalls which allow some movement forward and back, side to side, for shifting weight in travel. They have manger area, also at least 3ft, so they have LOTS of room in there. No faces flat on the front wall, because they DO have long necks, more than 3ft, in proportion to their large bodies and big heads.
I would be nervous of only having 7ft stall length on your horse. Once you fasten the butt bar, it could be too tight for her!
Any chance of hauling horse over to see the new trailer, “try it on” for fit? I did that with a slant load, which has since skewed my viewpoint of slant for big horses! She just did not fit! Dealer had all these numbers, that said she SHOULD fit. But with her nose pressed flat on the front of stall, the divider for two stall width would still not close! She was too long and too wide, even smashed into that double stall space. Such a good girl to even try! No way I would ever make her ride like that in such a trailer! She got backed out, put back in the old stock trailer and went happily back home in a trailer that fit her size.
Bad fit trailer can make a good loader into a bad one. And worse is horse trying to ride in there going down the road, fighting the trailer! Seen that before, very ugly.
