That would be a combination of a dragon with a bonnacon, which can emit a noxious excrement that can scorch its pursuers. Others say it is mixed with a poisonous gas. At any rate, it is forbidden to be used as a heraldic device in the SCA.

http://bestiary.ca/beasts/beast80.htm

A bonnacon eh? Now THAT'S something different. And I love the picture.

The heroine of the character is definitely only a small-team player, though she has gotten involved in large-scale battles before. So I see the role of the dragon as companion, more flexible than a fixed concept.

I had a look through that online bestiary that was posted, and came up with some good ideas for anti-dragon beasts. As for anti-dragon weapons- Lydia (Heroine) killed a dragon with a bolt from a heavy crossbow, but she had to poison the bolt. That was a bigger, dumber and meaner dragon though. Ballista are common in the books, used in seige combat and in naval combat, and could be employed against dragons. The Imperial Guard of one of the big Empires rides wyverns, which would be effective against dragons, though they do not breathe fire. There are lots of shape-changers and wizards as well, that can always call up demon-like things, or even the dragon-equivalent of flaming pigs (flaming seagulls?).

As for falling, well, it would have to be your biggest concern if you were a dragon rider, after mutiny :-) .I think the solution is going to be a roman-type saddle that is crouched in, with straps across the thighs/over the buttocks with some sort of quick-release. An Australian stockman's saddle arrangement might be good as well.

As for the heavy lifting idea, as in making it a dragon helicopter, that would certainly occur, but I think that a proud and rather vain dragon would not like to see itself as a heavy lifting tool, and might become a bit grumpy at always being asked to carry this knight here and that wizard there, and drop that troll in that ravine while you're at it. I think he will only consent to be ridden by one person, that he bonds with, like an eagle will imprint on a human, and carrying anyone else will be a matter of begging/negotiation/bribery with fresh meat.

I think the dragon's personality will somewhat mirror my heroines- she is very much the anti-hero. She does what she wants to do, and whatever it takes to reach the end she desires, without regard to good or bad. She is not much of a human really, which is why the dragon is attracted to her in the first place. She's not evil in the classic sense, but she's definitely not good either. If she does the right thing it is often either out of a sense of personal indebtedness or because she is being forced to by an external force.

Something which just struck me, an animal that is able to destroy vast regions of land and can kill whole armies and also is able to consume is enemies, will be subject to worship. Either as the deity itself or as a messenger of the gods or something like that - which is why the Egyptians worshiped the cat. That and because they all hate Mondays.
So if you are including religion in your story - which I hope, it is fantastically hard to create a "good" (in the sense of a realistic society that seems to be alive, not just stiff characters) fictional society without religion because religion has such a enormous impact on a civilization - there might be a battle against a tribe or whatever that happens to worship dragons.
That would be kind of a bummer for the soldiers, wouldn't it? They'd end up as a godly snack.
But then again, for such a battle, you need no anti-dragon devices.

Obvious choice for a Dragon Rider is Greek fire! You know, for when the dragon has a sore throat or is out of breath. Or for an unexpected 360 degree arc of fire.

Give the lance to the dragon, not the rider. Having a puny human hold a lance that'll impact with the force of two dragons flying at each other in attack speed never made sense to me and should by rights end with the rider having his/ her arm or entire torso simply torn off. Of course it could be fun to have just that scene play out just to prove a point.
And give the dragon a huge repeat arbalest pistol in a holstrer. With the poison tips of course.

Scott- I LOVE that shield LOL

He he he he- I think there's a place for a bonnacon in my books somewhere. That's pretty choice.

Monty Python would approve of your shield anyhow!

I suppose the French would have driven the English away even faster if they had hurled bonnacons at them!

OT: I would suppose that the medieval men would like very much the shield. They had a very gross sense of humor (we have to pass over the prejudices of the 1800)

I proved myself against dragons in writing, and in the end I eliminate it as a mount for my hero (I substitute him with a Incubus, a spirit of darkness. He can transform itself in a dragon, but he's not as powerful).
Probably a dumb (as a horse, or little more) dragon would be easier to manage, but not as interesting. From the other point of view you probably don't want to write another Eragon....

Thought of the day:
Come on, men: you didn't sign in the Guard to live forever!

Hmm. I seem to recall seeing a writing article that goes into some detail about possible countermeasures to fantasy aerial forces, including means that don't require the availability of anti-air weapons:

http://l-clausewitz.livejournal.com/399306.html

*looks away and whistles*

How about a harpoon with a tether that can be tied to a saddle horn. Now that's nasty.... :-)

I'll be sure to leave some feedback for the most-learned, well-spoken and erudite author! LOL

I actually went through a number of the articles- all very useful!