C.D.
Not pumping while you are at work will cause you discomfort and could lead to a blocked milk duct and possible mastitis. I don't know how many hours you are gone those work days but if you can at least pump one time this will help to keep up your supply, help to relieve the engorgement, and provide some milk for your daughter while you are away from her. Missing feeding will effect your milk supply over all.
From what you have stated you are only away from her working 3 days a week. If you are breastfeeding on demand when you are not working and including 1 morning pumping session each day along with the once pumping at work you may be able to provide enough milk for her, decrease your work pumping and not have to introduce formula (or at least give it minimally). You have worked hard to get breastfeeding off to a great start and it is worth taking the time to really see if there is a way to work around this.
Please check out the La Leche Leauge website
( www.llli.org ). You can find answers about managing breastfeeding and work as well as find a local LLL group near you. Talking to other breastfeeding moms will be so helpful.
Good luck!