D.W.
First, please don't doubt your ability to nurse your child or have enough milk. Breastfed babies will tell you what they want and need. And really you have no way of checking your milk production other than a satisfied baby. Can't tell by pumping and can't tell by the feel of your breasts at this stage in the game.
6 months is a very busy time of change and development. All baby's go thru phases where they have disruptions in their sleep or need more comforting from mom and dad. She could be going thru that 6 month growth spurt and needs to get topped off right before going to sleep. It's really not a big deal. Very common with breastfed babies to ask for a little snack to get topped off before going to sleep. Think about it-if she'd had a feed not long before that then goes back to the breast she's getting another round of the high-fat, creamy hind milk that is very satisfying to baby. No wonder she calms down and falls asleep.
Here's another hint-I understand not wanting her to get in the habit of falling asleep at the breast but I never found it to be a big deal with either of my kids. They both learned to sleep on their own by me sticking with their routine. But you can take her off the breast, burp her and then lay her down. That way she's got a little something in the way of activity in the middle prior to going down.
Once she gets thru this you can go back to your normal routine. Just be patient and follow her cues.