I know you have gotten a ton of replies, but I have to add my two cents.... as a breastfeeding professional, here are my experiences.
I know this sounds dumb, but make sure the nipple has a hole in it. I've seen a few (Playtex) lately that had NO hole.
Make sure the milk is really warm. Cold breastmilk sometimes clogs the nipples with the fat in it. Microwaving kills breastmilk, use warm water.
The softer the nipple the better. Ventaires have HARD nipples, but the Playtex with the drop-in's are very soft, so are the Dr. Brown's. The latex nipples (brown) seem to be the favorites. Also the wider the nipple, the better.
Remember, babies need to have enough of the nipple in their mouth to trigger the suck reflex. Get lots of the nipple in her mouth. Don't force her. If she is screaming, she won't eat. period. Calm her somehow. Then try again.
You may even have to nurse her for a couple minutes to get something in her belly so she'll be more willing to work with you. Try a time when she's nearly asleep and very calm.
You may have to try a few different bottles to get the right one. It is my experience that all the "breast" type bottles are not that much different than typical bottles. With that said, you may have to skip the slow-flow nipple, and go to a medium-fast flow. If your milk lets down fast, or she is a very efficient eater, the slower bottles may just piss her off.
Good Luck! I hope you figure this out quickly... if you need more info, or just want to pick my brain, give me a call!
____@____.com