It's wrong to sabotage someone's work.
Mia wanted to win the painting contest and Maya was the only real opposition.
Mia wants to win the contest.
Mia adds some extra details to her own painting to improve it.
Mia adds a tree to Maya's painting because she knows the judge hates trees.
Mia ends up winning the contest because of the improvements to her painting.
Mia ends up winning the contest because of the painting's added tree.