If you're having that much problems with skul, I'd recommend watching beelz to get the basic gist of things down. You'd be surprised at the amount of things you can learn from watching one of his runs
You should just be ready to jump anytime she slams down If you don't have an OP build/skul just take your time, attack when only one is on screen, whittle down both their health bars so when she buffs for the 2nd phase she has half health