Tezzy,
Maybe she's developing an aversion to the breast? I remember there were some frustrations early on, and maybe she's slowly just attributing those frustrations with breastfeeding?
Here's some info on Kellymom.com about how you can maybe help Ffion 'like' it again.
https://www.kellymom.com/bf/concerns/baby/back-to-breast.html
As an aside, my LO has been REALLY fussy at night (not really all day, just from 4-5pm to midnight or so. We cluster feed but what you describe Ffion doing, Sharlotte does it too. Feed for 5 mins, (of even just a few seconds) yank at the breast, pull off and scream her fool head off for the next 10 mins.
Over and over and over and over again.
I've found with Sharlotte it has to do with gas. If I don't get EVERY bit of gas out of her through burping, and do it several times during a feed, she's just miserable for the evening.
My dairy intake also seems to correlate directly with her fussiness too. But I know you've mentioned that you're already pretty much dairy free.