Atropos XR is normally designed to be fought solo. In Jets with a party of 3 she's not very dangerous. She uses attacks you'll recognize, as Robo has them too.

She will open with a single-target Rocket Punch. Next, she'll use Cure Beam on herself. Following this she will use Laser Spin (hits your entire party), Robo Tackle (hits entire party and cuts HP in half), then Cure Beam on herself again, then Uzzi Punch against a single party member.

After this she'll use Area Bomb several times until she self-destructs (message: “I… AM…”), which is also an Area Bomb attack, but it ends the fight. Dealing enough damage to her will also cause her to end the fight with Area Bomb.

As stated before, she isn't too dangerous, just keep your HP full. The challenge is more in defeating her as quickly as you can. Some players like to wait for her first Cure Beam to start dishing out damage. This is because if her Cure Beam heals enough to mitigate an attack against her, it saves time to not watch the animation.