mouth open while outside?

I've taken my juvenile female veiled outside the past two days and had a question. When she is out on top of her plant and basking, she will occasionally open her mouth for long periods of time. I don't know what to make of it. My best guess is that she is too hot from basking. The temp outside has been 75-80*F. The first time I saw her do that I just stared and tried to figure out what she was doing. When I saw it a second time, I moved her plant partly in the shade and misted her for 20 minutes. She was fine for a while after that, until she got back up to bask again for about an hour. She must really like that sun. The last time I saw her open her mouth briefly, like she was yawning. Then I misted her one last time for a good 20 minutes. This time She stayed at the top and enjoyed the cool mist of water. So I figure she was just getting a little dehydrated. Am I right to guess this? Also, do juveniles tend to bask themselves to the point of dehydration? Maybe they don't know their limits at this age?

She's probably just getting hot. Even though the ambient temperature outside may be 75-80*F, it's probable that the spot temperature where she is basking is much hotter.

The heat accumulates on her body the longer she basks. You should measure the spot temperature on her belly using an infrared thermometer. Then you'd immediately realise why she was gaping. It's usually much hotter than the ambient temps.

In general, provided you give them a way to get to a shadier spot where they can cool off, the cham should be able to thermoregulate itself.

But younger chams are far more prone to overheating, and so you should exercise caution when placing your juvenile out in the sun. It has often been said that chams can deal better with excess cold than they can with excess heat. Leaving a cham out in full sun, and with no way to cool down can be a very quick way to kill them.
So make sure there is always a shady spot for her to move to, and watch her carefully when she is out in the sun. They all gape a bit when it gets hot, but if she continues to gape for long periods, move her somewhere cooler.

I suspected that was the problem. Thanks for clarifying it. I'll move her to a shady spot and keep the mister going.

I open the windows everyday when I come home for my little guy, he gets all postured and proud looking, waves in the breeze then opens his mouth for a minute or so, he has access to any temp he wants, basking or shade. Im not sure why he does it!? Its almost like a huge breath of fresh air.. this is a work in progress btw, just started last weekend, waiting for my hibiscus and large branch to arrive to more cover and climbing routes! I cant keep him off of it tho.. I'm allowing early occupancy!