She should still burp for you. If you also nurse her, does she burp easily after nursing? DD seemed to burp easier after bottles because of the extra air.
I usually burp her either way. when she was a newborn it once took me 10 minutes to get her to burp, but she also used to spit up a lot when she wasn't burped. I would think with getting more air in from the bottle than the breast lo would need to be burped.
Re: when bottle feeding breast milk- burping needed?
DS only burps about 50% of the time after a 2 oz bottle but I still try to get a burp - maybe 2 minutes or so