Karla's always generated her costume from the moonstone, which forms whatever design she wants over her body. But once it's created it functions as a costume would until she actively orders it back to the moonstone, so Tigra's actions would affect it.
She can also reconfigure it with a thought, as she showed in her Meteorite days when she changed the design a couple of times. It's possible that she wasn't able to focus properly with all the popping flashbulbs around her so had to work with the torn costume.