Quaker biting at its legs

[emmy]

Hi, we have a female quaker parrot, Pippin, who is about a year old and up until recently has been a wonderful and happy addition to out family. But recently she has been biting at both her legs to the point they bleed quite badly and we don't know what to do.

We took her to a vet who gave her some iron as she was aneamic from blood loss and kept her for 2 or 3 nights to get her blood levels up but couldn't explain or provide advice to cure the odd behaviour. The vet also provided a plastic collar to stop Pippin from reaching her legs to bite them, although she still manages to.

She tends to just sit on her perch or our laps and not do anything and she barely vocalises anymore.
She is eating and loves apple but we are at our wits end about how we stop her self-mutilation.

We spend a lot of time with her but the biting did coincide with us not being at home as much for 4 or 5 days recently. Could this be the cause as I know parrots are very social. And if it is how do we restore Pippin to her normal happy self?