You don't have to break the law again to necessarily break probation.
The US legal system also thrives on plea deals. Prosecutors charge people with WAYY more than is fair, so the risk of going to court is too high (years in jail) and defendants are bullied into plea deals that suck.
If you'd like to learn more about how messed up this system is, season 3 of the podcast Serial is a pretty good starting place.
In a case like this, there's no "time" to do. It's not as if this girl narrowly avoided incarceration on the condition that she agree to probation. Probation was the "time." Her offenses didn't qualify for a term of incarceration.