I have a rather challenging DS. I think DD is my reward for not strangling him some days

With TT him, I took his lead. At kindy, they put all the kids on the toilet straight after every nappy change. One day he just started doing wees when they put him on so we carried on at home from there. We made a big deal of it - "If you do a wee on the toilet, you can wear your big boy undies!!!" and if he did a wee "Yayyyy Claps for DS". He has always refused a potty so we got him a little step & seat for the toilet which he was excited about. Now he won't use the seat either. He reckons he has a "big bum" so he'll only sit directly on the toilet. Ah who cares, he's using it! We still struggle trying to convince him to sit on the toilet some days but he is improving. We are only a few months in though so accidents are to be expected.

Maybe introduce her to the toilet slowly when you change her nappies. One day it'll click. I wouldn't try to force it on her though, if she's not ready.