If you're not yet familiar with it, Fiona's Grand Divider (236A etc...) has "clean hit" properties. Essentially, you have to time the actual hit to be within a certain area to get a clean hit and maximum dmg. I don't play Fiona so I don't know the actual window for the clean hit, but I do know it's way harder to get a clean hit on the super version of the move than on the regular one. The dmg is EXTREMELY high and can result in an instant KO if done with steel powerups. (seen here at 2:50)
A basic Fiona bnb is:
2A-2B-2C->HC6-5B-(IAD)j.A-j.B->(land)j.A-j.B-dj.A-dj.B-dj.2C
or alternatively:
2A-2B-2C->HC6-5B-(IAD)j.A-j.B->(land)j.A-j.B-dj.A-dj.B-dj.C-dj.214C
As per your reference to 214C, I assume you mean Heaven's Fall (j.214C). The main issue with using j.214C is that it leaves you at no advantage. Sure you get decent dmg, but both you and your opponent recover at the same time and you're pushed away from them. I'd say to try and avoid using j.214C and go for j.2C.
However, if you still wish to use j.214C, just do:
Fire arcana (corner): 3[C]->5[D]-j.B-236D->j.C-236D->j.C-j.214C
For more Fiona info, I direct you to her page on the arcana wiki.