Actually that cage is too small for 2 budgies........let alone 4. 4 budgies need at LEAST 15,300 cubic inches (times height, length and width)

They may be fighting for space, breeding rights and general "best space in cage" Females have a rep for being a bit agressive. And seeing how when you brought the males in the budgie started to get agressive i would say she wants everyone to know she is top bird. She may not be loney alone, if she has toys, plenty of outside time and wated interaction with her other birdies

New pics soon smile