I just spent a few minutes testing possible counters to his sword dive in training mode. Dia (BD) will beat it out clean on reaction, you'll absorb the sword hit and knock him back as well, at worst you'll absorb the hit and you'll both recover at about the same time. You can also tag him with crouching B (direction depends on spacing) or j. B and knock him out of the attack. Dia will be your best bet to counter sword dive tho, heal and room to breathe.
As for keeping him off of you, utilize dashes to stay out of the corner and Dia to keep him out of your bubble. Don't be obvious with this or else you'll get baited and punished hard for it. Also, never do Maragidyne (236236A) when he is close, if he has meter he will use his lightning sword super and if not he can just BD you, both on reaction. Smart zoning with fans, 236A/B and 236C/D (remember to hold it for manual releasing) and tons of patience will net you the match. Personally, I think this one of her toughest matchups and will severely test your skills as a Yukiko player.