Sorry Nigglenaggle, but expressing is not a good way to guage how much a baby takes at a feed. A baby will always be more efficient than expressing, but will have fluctuations in nutritive and non-nutritive sucking during a feed.
It's also perfectly normal for babies to nurse for nutrition, hydration and comfort during the night at 6mo and beyond (way, way beyond!)
Whenwill's method echoes some hints given in the No Cry Sleep Solution by Elizabeth Pantley - a very lovely gentle pro-bf book to help babies get better sleep. 6 months is a little early to encourage total night weaning (not usually recommended until 12-18mo), but you could certainly take a few tips from a book like that.
As it is perfectly normal for babies to continue night nursing, it's often easier to try and change our behaviour than our babies (who, after all, can't read parenting books, can't tell the time, and only know they need you in the middle of the night for whatever reason). Do you co-sleep? If done safely it's a great way to get more sleep.
She won't night nurse forever, so some minor adjustments could mean a more restful night for everyone without any tears and tantrums (from either of you :))