I found with my son that he would want to nurse more often (I don't know if you nurse on a schedule or if you just know when she will be hungry for pumping at work). I didn't nurse on a schedule- this allowed my son to nurse more often when my milk supply was a bit low (this helps build it up a bit).
If you notice your girl wanting to nurse a bit more when you are with her (maybe it might be even annoying the amount she wants to nurse), she might be helping to build your supply. The reason I mention this is so you know what she is doing (if she starts to do this) and not to be annoyed but to know she might be helping correct the situation herself (it normally will only last a few days (1-3) and she would be back to normal nursing). If you nurse on a schedule you may not get this response from her (so she may not be able to self correct the problem).
When I was "low" my son would nurse a lot and this would help correct the problem.
I mention the above as my son helped correct the problem himself and I didn't have to change much. Also if I was ever "out" (even though you are really never out), I would wait 20 min and start again (I would distract him for 20 min) then my body would be "full" again- at least enough to finish the nursing session.
Also, is your daughter complaining or are you just felling not as full? Because sometimes the body adjusts (just so you aren't overflowing anymore). You might think there is problem but it might just be your body adjusting and not an issue at all.
You aren't going to dry up and if your child isn't getting enough she may want to nurse more during the day. Sometimes they will cry or complain if they feel you are "out", but like I said I would just distract my child and try again in 20 min.
Also, I would definately check your pump see if there is a better one. You can maybe add extra pumping sessions (or I think if you pump longer sometimes this helps- but I forget, I think I tried to pump longer and that helped).
Also definately check how much you drink & eat. I tried to cut down on how much I ate at one point in time and I saw it dramatically decrease my supply. Same with Water- drink more that helps.
Just FYI I actually got to the point where I would only pump once a day and then sometimes not at all and my son would be ok (sometimes he would nurse a bit more on the weekends or when I was there to help bring up the milk supply). So Again just mentioning this because sometimes your child will help self correct the problem.
Here are two websites that might help with info: