Lack of calcium/phos/D3/vitamin A in the right balance and improper UVB are mostly the cause of this. The bones are weakened and the muscles are as well at this stage of it and so she can't control where her feet are going...and if you look at her arms, they are not straight because the bones have likely broken. There are other things that are affected by this as well.
You really need to see a good chameleon vet so you can get some liquid calcium gluconate. She will need this in addition to proper supplementing and proper UVB, proper temperatures, etc.
How old is she?
Has she ever laid eggs?
What supplements do you use and how often for each? Phos, calcium, D3 form of vitamin A in each?
What specific UVB light have you been using?