For the Dancer I don't advise using a shield unless it's something like Morne's Greatshield with ridiculous stability.
You should always keep your distances from the dancer as her flurry of attacks can be extremly hard to dodge for a beginer, try putting at least half of the arena bettwen her and you.
The attacks you can retaliate after are:
-The spining dance she uses when she goes into 2nd phase, wait for it to end then get 2 hits on her. Alternatively you can synchronize your rolls with her swings during that combo, not only will you look super stylish while doing it but you will also be able to get 3 hits on her.
-The attack where she thrusts her sword into the ground to create an explosion, wait for BOTH of the explosions to occure then run to her and get 1 hit on her
-The two attacks where she swipes her sword to create a barrier of fire/dark infront of her, you can get 1 or 2 hits on her if you can get behiend her
-The attack where she does an uppercut slash with both of her swords, dodge the attack and get 1 or 2 hits on her
It is important to keep your distances as the dancer is one of the least mobile bosses of the game, also her jumping attack is followed by a very fast spinning attack so just run away when she uses