Dancer is down!
It’s taken me about ten days (four of them, admittedly, on a break), two attempts today, two embers, two divine blessings, two each of the fire resin and lightning resin, nineteen estus in total and eventually she went down with three estus remaining. I’ve not really enjoyed the experience of the boss that much but the cut scene afterwards with the decapitated Knight statue was pretty cool.
The weapon I used eventually was a simple longsword (+6) and a Pontiff Knight Shield.