Mare won't let anyone mount

So there's this TB mare that is fresh. She's been started perfectly from the ground -- sacked out, not spooky, longes, takes the bit, takes the saddle, and acts like a dead broke horse... from the ground. Then, you go to get on her, and she will jump away and sometimes kick out. She has never been ridden successfully, mind you. The few times she HAS been ridden have resulted in hard falls from her bucking frantically. She's a very sweet mare otherwise. What to do, what to do?! Did I mention she's 17 hands?

Where the heck is a cowboy when you need one..Ha!

Maybe break it out into smaller pieces for her? Do that exercise where you bang around the stirrups and pound on the saddle with your hand a few times to get her used to movement in the saddle without an actual human up there. (do not stop until she's standing still and relaxed - follow her around the ring if you have to while banging on the saddle)

When she's good with that, just put weight onto the saddle for seconds at a time. Literally lean over it while still standing on a mounting block, so again you're safe if she freaks out.

Next step would be to get on, but then get right back off. Reward her for standing quietly.

I am not a trainer and don't play one on tv. It's just what came to mind. She's 17 freakin' hands, so if it's really dangerous, please bring in a expert to help her past that problem.

I would be searching hard for something that is causing her pain once a rider's weight is added to the equation. Has she had a vet workup? Has a chiro seen her? Does her saddle fit her (not only through the gullet, but through the panels, length, etc.)? Saddle fit can look passable without a rider, but really go downhill once there's weight in it. You didn't say what style you ride, but if you're riding English is it possible that the flocking has lumps that could be digging into her?

I've never owned a mare, so take this for what its worth, but I have heard/read that ovarian cysts or similar issues can cause them a lot of discomfort, especially when the weight of the saddle starts pressing on their backs.

It's very possible that it is a training issue, not a physical one, but ruling out the physical tends to be a good place to start.

She has carried dead weight in the saddle (jeans filled with sand) for miles. She is not sensitive to flapping the stirrups, hitting the saddle, etc. She loves people. When I was trying to mount, because she refused to stand still, I tried to pull her nose to her side to keep her from stepping off. Eventually this just led to relentless circles, and the horse got very frustrated (even when I let her head go). What's strange is she would nudge me away with the bridge of her nose and open her mouth and reach for me, but never bite me. It was just like "Please, please don't... I don't want you up there, you might get hurt." It was kind of sweet, yet very frustrating... vet has checked her. She isn't sore. She has done the prerequisites for riding and passed beautifully - the next step is a rider, that's it!

Her first ride was a green-ish rider (rides for pleasure, can hang on but not really what you'd call "experienced"). Since she'd done her groundwork so well she didn't seem like a horse you needed to worry about on a first ride. He rode her just fine but accidentally goosed her side (kicked her a little too hard on accident) and she got scared and took off bucking. Each subsequent fall since has led to her just refusing to let anyone on. I think the rider falling off scares her... understandably...