Maybe there is more to it then just a glass door. Some more pictures of the actual inside would help. Glass is of course not a barrier they understand but assuming that the cage is of adequate size perhaps the inside is not up to par for her. Lack of branches, vegatation, as roo touched on temperature gradients could all be reasons to look for a new spot as far as chameleons are concerned. If the cage is small she could be seeking more territory.
I do think that a screen door would not hurt if possible on the cage you already have if you want to retain it for awhile longer or permanently.
Jewel the cage looks great.
. He not so much scratches but ' pads ' the glass with both front feet. The second I raise my hand to open the viv door he gets all exicted and positions himself one foot stepping forward in anticipation to step onto my hand. 
but I am happy he is ' Knocking the door ' rather than any form of distress. His 'patting ' isn't random..it's done at clear defined times / reasons and he scampers out like a school kid at break time 
Mine does this but only when I come towards him / his viv and then when he sees the wax worm pot
He is the 3rd Cham I know to do this in the UK...all kept in different vivs, glass, mesh or a mixture.
Mine is wood and alternate mesh panels, offering 3 way airflow. Only the doors are toughened glass and they are only top half length and the bottom half of the front has the glass removed completly and replaced with mesh.
If I am below him giving a waxworm to my BD, he climbs down and does the same ' padding ' on the mesh. He simply wants out to play.
Ok he is a very sociable Cham and much prefers sitting on his tree with me while I iron in the kitchen
That was a nice read I swear he sits and waits for me / waxxies. 
