Ender Dragon Fight

So, I am playing Minecraft java 1.14, and I cant defeat the ender dragon. Every time she comes down the bedrock structure, I can hurt her. But, once I hurt her once, she just picks one of the obsidian towers, (I already destroyed all of the crystals) and circles it! If I go near her then she launches me like hundreds of blocks in the air! Then she doesn't come down anymore. Also, when I tried save and Quitting, (I even closed off the main menu) but then she had full Health again!

 

Please Fix, so I can beat the game. 

-Jacob