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A probation violation for driving on a suspended license is one thing. And it's pretty common because most people who have trouble following the law to drive their cars not drunk, not speeding etc in the first place generally have trouble following the law not to drive also.
That's just reality. But it's equally true that even with a probation violation the offender is not very likely to serve out their original sentence either. More likely the probation department, the DA and the judge will agree that perhaps sending that person to a few weekends in jail is a compromise. It's the defendant's attorney and family to convince them of something else. And that's usually an increase in your probation time.
The thing you REALLY don't want to do is piss off your P.O. Really. Those people have an awful lot of power over you. If you violate your probation the first thing you have to do is call your P.O. and beg for mercy.
In practice though it's unlikely that the original sentence will be enforced UNLESS what you do to violate probation is a worse crime than what got you on probation in the first place. Say you get a DUI, get 1 year probation and lose your license for a year. If you reoffend before that it would take some worse crime, e.g. a DUI with an accident, or evasion or some other unrelated thing like theft or gun possession for the original sentence to kick in.
The fact that Ms. Hilton was originally convicted of a DUI is almost besides the point, legally. Reoffending by a simple driving on a suspended license is not really sufficient to kick in that original suspended sentence. Typically that would result in a longer license suspension - say 3 - 5 years.