I'm not sleeved yet, but I am a professional Lactation counselor. DO NOT WEAN! Just nurse as ofter as your daughter wants. Fenugreek is only slightly effective in increasing milk supply and I would suspect that any fussiness you might be seeing and interpreting as low supply are actually baby's reaction to the flavor of your milk. This is not a concern for her. Your caloric intake doesn't change the quality of your milk at all. In fact women in countries where this is severe famine are often seen with fat little babies on their hips. Your body will take every it has and put it into milk for your little one, just as it would for pregnancy. This is of course an issue for you and you should try to boost your Protein after the surgery (my nutritionist suggested putting greek yogurt in my shakes to up the protein by about 10mg a day). Unfortunately the LLLi leader you spoke with may be using old info. We don't need alot of calories to make milk, and we absorb far more calories then a non lactating woman would. We have alot of new info that is breaking alot of the old beliefs but the old beliefs do still persist.
Keep in mind that babies go through fussy periods that have nothing to do with supply, such as at around 6 months they have a "growth spurt" where they nurse all day long and all night long too. If you have not had a period PP yet that can also be on it's way back and causing you to dip slightly. This is ok and normal. Also they get to times when they re JUST about to do a new milestone and they will nurse nonstop, ditto with teething for some babies. Just roll with it, it's almost certainly not you.
Some things that may cause supply issues are birth control pills which are often recommended after surgery because of our increased fertility once we start losing weight (this includes progesterone only products), and lack of time nursing. Things that do not decrease supply are not eating enough or drinking enough (lots of research has been done on this, honest). Here is an awesome way to boost supply (without digging into your freezer stash), power pump. To do this, set up your pump and turn on the tv. When there is a commercial turn the pump on and pump. When the commercials are done, turn it off. Rinse and repeat for 30-60 min until you've seen 1-2 tv shows. This high frequency, short duration pumping schedule tells your body you have a set of starving twins and to ramp up production in a hurry. If you do this and let your daughter eat as often as she wants you'll be back to a full supply in no time. There is no reason to believe you need to wean or that your milk will change, but doubt and supplementation are a sure way of decreasing the feedings you give her for which will lower your supply. Keep up the great work and congrats on nursing this long already. I'm sure you'll be able to make it to a year and as long as you want to nurse as long as you keep it up.
Lucia (CLC, and mom of 4 breastfed babies including a set of twins and a singleton who will be nursing when I'm sleeved)