She couldn't put the book down until she finished it.
Meaning: This means she was so interested in the book that she read it all the way through without stopping.
Choice of Words: Put down means to place something in a lower position or to stop holding it. Finished means to complete something or bring it to an end. When you combine them, "She couldn't put the book down until she finished it" means she was so engrossed in the book that she couldn't stop reading until she reached the end.
Alternative Expressions
Related Expressions