D.W.
What you are able to pump and what baby is able to actually get from the breast are two different things.
But she has other things going on. Eating from the bottle is easier than breastfeeding. Try using the playtex nurser with the latex nipple in slow flow. That is more like the breast.
But putting her to breast more often may help. Make sure that she is getting the areola in her mouth. You may need to offer her the breast more often than what you were used to with your other kids until she gets it.
Here is some good info on nipple shield use and how to wean from using it as they are not for long-term use:
http://www.kellymom.com/bf/concerns/baby/wean-shield.html