Aviary Budgie Struggling To Fly

Hello, 

I am new to bird keeping and am currently keeping a cockatiel (indoor) and 4 budgies (aviary).

I have begun to notice that one of my budgies has been struggling to fly more and more. When we first got her she already struggled to fly and recently has been getting worse. This has been going on for weeks and it seems that she attempts to fly up or down between perches and as she can’t fly properly, lands on the ground heavily. This seems to result in her wing feathers repeatedly breaking on the rocks and shell grit that make up our floor.

I am unsure of what to do in this situation as I cannot supervise them all day. If anyone has any ideas, please let me know as I am worried about her and a cold winter is not far away.