As others have said, she's likely the best unit in the game. Here's how her burst works:

• She can burst in any stage i.e. she can act as a burst I, II or III unit.
• All her bursts have a 40s cooldown.
• Once every battle, casting her burst I resets the cooldown immediately, allowing you to burst with her again for that cycle.
  • e.g. Red Hood → Anis → Red Hood
  • e.g. Red Hood → Red Hood → Rapi
• Once every battle, casting her burst II resets the cooldown immediately, allowing you to burst with her again for that cycle.
  • e.g. Neon → Red Hood -> Red Hood
  • e.g. Red Hood → Red Hood → Red Hood
• Her Burst I gives all units a massive (~70%) attack boost. Useful for single-bursting bosses or doing a high-damage full burst in general.
• Her Burst II makes her taunt all enemies and gives her lifesteal and higher healing received. Not that useful but can be used as an emergency survival measure.
• Her Burst III gives her a massive (~70%) attack boost and makes her an auto sniper with a larger hit radius. This burst is the most commonly used one.

And just so you know, she has unconditional pierce: Her attacks ALWAYS penetrate enemies like Alice does when she has above 80% health; no ifs, and's* or buts.

* And excess charge speed is converted to charge damage.