Revealing mistake: When Tigress is hatching a plan to escape Gongmen Tower after they have been trapped, she looks out over the wall. But take a close look at the archers: they all move in perfect sync, indicating the same animation models were used for all of them.
Continuity mistake: When Po and the Furious Five are in the top floor in Shen's palace, the lights above them are brightly lit. After Mantis smashes the cannon through the floor, the lights turn off.
Answer: More than likely she wasn't in the tower when it was destroyed. She directly confronts Shen about destroying the tower and makes no mention of having survived it's collapse. She only comments on his recklessness in destroying his ancestral home.
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