It means she had become addicted to acting. She loved it so much that she couldn't stop doing it.

online Collins dictionary - "bug" meaning #6 https://www.collinsdictionary.com/dictionary/english/bug SINGULAR NOUN [oft noun NOUN] You can say that someone has been bitten by a particular bug when they suddenly become very enthusiastic about something. [informal] I've definitely been bitten by the gardening bug. Roundhay Park in Leeds was the place I first got the fishing bug.

I agree with Claire. Enjoy something so much it is "addictive".

Literally, it means she was infected with a microbe. But figuratively, it means she found something that she was very interested in, something that she liked a lot, in this case, acting.

"she caught the bug" is usually slang for when someone gets sick from the flu. So in this case it's a metaphor, she tried acting and was infected with her love of doing it and can't stop.