How do you normally burp her (as in what position)? If you burp her after a full feed, does she through up a lot of milk? Did the doctor prescribe colic drops for you?
My son was colicky as well. He was on colic drops till 5 mths. I burp him twice thru a feed and if I burp him only at the end of the feed he would throw out milk (mild reflux).
I suspect your baby rejects milk after being burp because of the pain. Colic drops help to combine the smaller air bubbles in the tummy to big ones so that the child can burp it out at all at once.