Probation Violation

State of occurance: Pennsylvania

My sister was arrested several months ago for possesion of heroin (small quantity). She was given six months of probation, and if no further violations occured, her record would be expunged (first offense).
She was recently arrested for possesion of marijuana (less than 5 grams), which of course, is a violation of her probation. She is in the process of hiring an attorney, and is placing herself in a drug treatment program. My question is, is it highly likely she will receive a prison sentence?

My guess is that she will receive jail time for one or both of her crimes. She is correct to hire an attorney and seek drug treatment.