The overall temp is probably too hot. I've only had my cham for a month so I'm not an expert but I noticed that he would keep his mouth open while basking if the room temp was over 75-77 degrees. I've lowered the room temp to about 71-73 and I haven't seen him open his mouth since. It also may be that her nostrils are clogged with salt deposits. This isn't a problem as it happens naturally but you could try washing them off and maybe she'll breathe through her mouth more. Hope this helps