Very Old Female Beardie Biting Off Her Own Toes?

[Shadowpika2]

Hey any help with this one, I have an old female (like really old like 15 or so old.) I was given 5 years ago. She has started to attack her toes, she has just finished shedding and she had some skin so I washed it off and cleaned her up but the next day she was biting her own back leg toes off. I have washed her again and disinfected the foot but she just keeps attacking it, even when I bandage it. She is well fed and has no build up of scales on her toes.

What should I do? Thanks