cage - in the first 2wks you have to restrict her movements; that is to avoid her getting into rough plays with other dogs.
dog food, just continue to give her the usual dog food; change into puppy food should be gradually done entering the 2nd month of her pregnancy.
vitamins - just give her ascorbic acid until the 6th week. entering into the 7th wk, you need to give her supplements specifically for gestating bitches, you might need to ask your vet what is best for her. i have my own supplements but your vet might suggest better ones.
raw chicken - if she is used to it, why not? but if this gonna be the first time that you'll be giving her that, i suggest not at this time. allergies might occur and that will complicate matters for you and your bitch.
bathing - yeah of course you can; it'll keep her clean and cool. just limit the bathing the shortest possible time so as not to stress her much.
letting her play with other dogs - this should be supervised. if things getting rough between them, isolate her immediately.