Cara took Tina’s mask, because she wanted to fix it up, make it better.
How do we know? Cara knew information about the mask (it didn’t have metal over the nose) that no one else knew. She was hiding something behind her back, and we know that she has the ability to make/ fix up masks.
She was planning to fix it but got annoyed that she didn't have enough time to fix it before they found out it was missing.