If we fight we might be best off doing it right now. True, we could regain spells and such, but those beholders are fairly tough. With a dozen of them blasting away at her she has to be taking some damage. We have a little time to prepare/move and there are a bunch of real threats on the other side. This is the opportunity. There is likely no way to set a trap for her.
Is there a way to collapse the cavern roof on her? And, of course, not on us. And, of course, let us be able to dig out the heart afterwards? And, of course, not give her a chance to move? Probably not, but thought I'd ask.
I like the idea of not fighting. I've been wondering for a while if it was possible.
Is there any chance this IS the Dragon Queeen? Just before we met her and in a different form? I suspect not, but since I wasn't in the game when she was, I don't know. They can change shape, so size seems doable for something this powerful.
As for talking to her, I think we want to let her finish the beholders first. And we might want to let her have a moment of freedom before we approach. Perhaps standing atop a hill a ways a way where we are obvious, but not right near would allow us to be spotted, present no threat, and talk a bit before her immediate response of "kill" wipes us out. As for the best way of communicating, a skywriting spell would certainly be nice. Anyone got such a thing? But I think just yelling from a safe distance would likely work. As Tann said, her senses are good. And she will be smart. Getting her attention and not attacking might make her curious.
The fact that she was imprisoned by these beholders is still a curious thing. Giant (red?) dragons don't have a habit of being good in my esperience, but the enemy-of-my-enemy sort of thing offers a bit of hope.