i love budgies (be very careful not to let them get out of your house though you will never see them again) i had an inside cage and i had an outside flight cage but they never liked it i had a boy and a girl who had two babies that i sold. i fed them basic grains and seeds and i also sprouted...
hi when i ran out of a grain based food and i could not find any i put my chickens on layer pellets they hated me for it so i put a different feed that had grain and pellets after i ran out i put them on the layer pellets (i mixed it wheat for about 2 weeks) they where fine with it
good luck
if she has the mind to hide the eggs she will be a great mum if she is strong it will be fine to leave her with the flock (in the old coop if they are together)
the chick should be fine you can splint the leg but you might as well just leave it
good luck keep yourr fingers crossed
tonight or tomorow night you should put the new hen on one of the roosts aparently when they wake up they dont fight as much but you will just need to let it play its course she seems to want to be leader.
but if after a month they are still fighting you may need to get ride of her
good luck...