Why is my rabbit so aggressive?

She is a spayed female and she lunges, nibbles and growls at me. Some times its when my hands in the cage or just when im holding her. She has a good life, greens every night, a huge cage indoors etc... Does anyone know why she is doing this?
Update: I know for sure shes not pregnant and i got her from the SPCA they didnt know how old she was.
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