I would also suspect that she is about to come into season, bitches can be very badly behaved around that time, have you noticed aything in particular that starts the fighting? is it over food or possessions? or excitement such as before a walk or when visitors arrive?
Whatever the cause just be sure not to leave them alone together unsupervised until it's sorted out
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Kay, pet portrait artist and Mum to Milo and Fred, foster mum to "Tabatha Snow" aka Maggie
............ all run ragged by the chooks Myrtle and Mavis
www.pettpaintings.com