Her jealousy could be portrayed in her words as well. She might make sarcastic comments to the person who is the cause of her jealousy. In a fanfiction, if she's jealous of a new kung fu prodigy, she could say things like 'Just because you can do a few flashy moves doesn't mean you're a real fighter' in a rather bitter tone. Also, her body language could be a giveaway. She might cross her arms and turn away when the person she's jealous of is around, like when Po is getting praised for something new he learned.
Tigress' jealousy could be shown through her actions. For example, she might avoid Po or the person she's jealous of. If it's about someone getting more attention from Shifu, she could give cold stares during training sessions.
In a Kung Fu Panda fanfiction, Tigress' jealousy would likely be a complex emotion. It could start subtly. Maybe she just trains a bit more intensely when she notices someone else getting special treatment. But as her jealousy grows, it could affect her relationships. For instance, she might not want to participate in group activities if the person she's jealous of is there. Her facial expressions would be key too. A slight frown or a narrowing of her eyes when she sees the object of her jealousy succeeding or getting attention. And over time, she would have to deal with this jealousy, either by confronting it or learning to accept the situation, which would make for an interesting character arc in the fanfiction.