Constant bullying may not be the best approach. 4-5 HP characters even with 0 defense can survive shots with ease and do damage back. With this in mind, ignoring players with more than 3 HP can be better. The player should focus on Encounter panels instead.
Since Star Breaker can't use stars as a win condition, try to prioritize Encounter panels early. Once a player hits their fourth norma check, the Boss panels show up, and it will substantially more difficult to get wins until the boss is defeated. Thus it may be a good idea to avoid getting to the 4th norma check until another player has.
Cards that can reduce other players star totals, such as Flip Out, Unlucky Charm, and Scary Solicitation, help slow down star progression for other players since gaining stars isn't as important. Dark Side of Business can steal massive amounts of stars from a player that's marginally ahead of the others because of Star Breaker's base stats.
Gentleman's Battle, Piyopiyo Procession, Invasion and Assault allow Star Breaker to easily engage in battle, which she needs to do because she is so heavily reliant on wins. Party Time can create chaos and give some wins depending on the turn order.
Along with the previous tip, Lonely Chariot, Dash!, and Windy Enchantment increase movement to close the gap for more combat opportunities. Lost Child and Ambush also allow creative alternatives to catch some players off-guard.
Pudding and Quick Restoration will keep HP topped off. Star Breaker has a recovery of 5, so staying healthy can prevent being KO'd and therefore reduce turns wasted on revival.
Wanted can allow Star Breaker to receive extra wins if she KO's the player who landed on the trap.
Path Blockers can be invaluable for causing other players to land on your traps, which can add an extra element of strategy with Invisible Bomb traps, which are hidden to other players.
Sealed Guardian can be used as a good way to burn stars, as well as reducing players to 1 HP, making them easier to KO.
Summoning the boss with Oh My Friend stops Star Breaker from getting easy wins from Encounter panels. NoName can also use Overseer to accomplish the same goal.
Surviving combat against Star Breaker is very important, because unlike Encounter panels, players give two wins upon defeat. Characters with high defensive stats and cards such as Tactical Retreat and Shield will drastically reduce the chances of being KO'd. Warping with Here and There will sometimes create distance as well.
Since Star Breaker's bombs count as traps once they're set, Star-Blasting Light will wipe the bombs off the board and can do massive damage to Star Breaker herself.
Encounter panels instead.
Boss panels show up, and it will substantially more difficult to get wins until the boss is defeated. Thus it may be a good idea to avoid getting to the 4th norma check until another player has.
Flip Out, 
Unlucky Charm, and 
Scary Solicitation, help slow down star progression for other players since gaining stars isn't as important. 
Dark Side of Business can steal massive amounts of stars from a player that's marginally ahead of the others because of Star Breaker's base stats.
Gentleman's Battle, 
Piyopiyo Procession, 
Invasion and 
Assault allow Star Breaker to easily engage in battle, which she needs to do because she is so heavily reliant on wins. 
Party Time can create chaos and give some wins depending on the turn order.
Lonely Chariot, 
Dash!, and 
Windy Enchantment increase movement to close the gap for more combat opportunities. 
Lost Child and 
Ambush also allow creative alternatives to catch some players off-guard.
Pudding and 
Quick Restoration will keep HP topped off. Star Breaker has a recovery of 5, so staying healthy can prevent being KO'd and therefore reduce turns wasted on revival.
Wanted can allow Star Breaker to receive extra wins if she KO's the player who landed on the trap.
Path Blockers can be invaluable for causing other players to land on your traps, which can add an extra element of strategy with 
Invisible Bomb traps, which are hidden to other players.
Sealed Guardian can be used as a good way to burn stars, as well as reducing players to 1 HP, making them easier to KO.
Oh My Friend stops Star Breaker from getting easy wins from 
Overseer to accomplish the same goal.
Tactical Retreat and 
Shield will drastically reduce the chances of being KO'd. Warping with 
Here and There will sometimes create distance as well.
Shield Counter won't be able to one-shot Star Breaker if she has 
Super All-Out Mode or 
I'm on Fire! activated. However, it will still end combat.
Star-Blasting Light will wipe the bombs off the board and can do massive damage to Star Breaker herself.
