Thanks for your input. I have used both stock and slant trailers...my friend has an open stock that he converted to a slant but I always leave it as open stock and my trainer has a slant with a rear tack. She loads in the slant ok...little hesitation occasionally but always goes in fairly quickly and without incident. When I loaded her in the stock 2 weeks ago, it took us 30-45 minutes to get her in and she's been in that trailer a few times. She was moving around a fair amount in the stock trailer as if she was having trouble keeping her balance. I need to get her a mat, but she does have occasional light lameness trouble so I would like her to have something to balance against.
Regardless of the trailer, she is always drenched with sweat by the time we arrive. We keep our trailer trips local and short for now as I'm hoping her anxiety will ease in time. She's pretty quiet in the slant, every now & then she will get antsy if we don't get moving soon, but most of the time she will stand quiet in the slant when parked and when moving.
I'm going to look for front tack to help her anxiety with the initial loading, and a fairly "open" trailer with slats and plenty of light/visibility for her as I think anything else will only add to her anxiety. Our sport is trail riding and so its important to me for her to be comfortable in the trailer.