I was thinking about how you said your daughter will only latch on for about 30 seconds--I wonder if that is because she has gotten used to the instant flow of a bottle and she doesn't realize anymore that it can take a few minutes of sucking before the milk really starts flowing. This may be why she nurses better in the morning, because when your breast is more full, the milk starts flowing sooner.
Your supply is probably a bit down at this point because she is not nursing so often, and you shouldn't cut out the supplements cold turkey. (A Lactation Consultant may be helpful in devising a plan to wean off the supplements.) You might want to keep latching her on a few times in a row (as long as she is willing) and hold off on giving her something else right away. Do you sleep with her? If you don't, you might want to try that just for a while because I think 1) the more you can encourage her to nurse, the better and 2) I think just the physical closeness can help up your milk production. Also, I have found that Mother's Milk tea (by Traditional Medicinals) really can help increase your milk. I have a friend who because of hormone imbalance has trouble producing a full milk supply and she said that really seemed to make a difference for her too. (I just thought of something else: Have you ever gotten your thyroid checked? Low thyroid can cause low milk production and sometimes the symptoms are so subtle, you may never know there was a problem.)
And as someone else said before, even if you just continue nursing her once a day, she is getting a lot of benefit from that. I get the impression it may be all of the pumping that is getting you down, and as I said before, a pump can't do it like a baby can, and even if you have a top grade pump, they do lose effectiveness after a while.