I am a working nursing mom as well. I attended a breastfeeding support group at Glendale Memorial Hospital regularly when I was on leave. The group meets every Thursday at 1 p.m. They have a scale there and you weigh your baby before and after they eat, so you know exactly how many ounces they are taking during a feeding. Babies drink until they are full on the breast and then they stop. With a bottle, they will often drink until the bottle is done, regardless of their hunger level. It is possible that your daughter is getting less on the breast than she is getting with a bottle.
There is also a breastfeeding support group at Holy Cross in Mission Hills, which is closer to you. At least for the one at Glendale Memorial, you don't have to have delivered there and it is free. You should call and find out if it is the same at Holy Cross.
It is also true, however, that a baby can get more milk from the breast than a pump can. If you think your baby is getting more milk by breastfeeding than you are able to produce pumping, you may want to try renting a hospital grade pump for a month. They are more efficient than the regular grade (though not as good as the actual baby). Also try taking fenugreek and blessed thistle to increase your milk supply, available at Whole Foods.
To rent a hospital grade pump, go the the Medela website. You can search there for people who rent hospital grade pumps that live in your area. You could also rent a scale for your baby there too if you can't attend the support groups and want to get a good sense of how much your baby is eating.
Working and breastfeeding is quite a challenge. Pumping can be quite a chore, but it is so worth it for both you and your baby! Keep it up!