Telling a student she’s the problem without telling her.

I have a junior class that is noticeably different when one particular student is absent. She’s not a huge discipline problem herself - it’s hard to describe without seeing it yourself, but she just brings the behavior and effort of the rest of the class down.

Last week she was absent three days with the flu and the class was calmer, more productive, and there were few if any discipline issues.

I’ve noticed this before on days she is absent. Is there a delicate way to tell her this? Or should I just focus on rewarding and praising the others when they are actually focused?