Yes, I would concur in your assessment that she may now have to face some time in the slammer(having apparently commited again the very same offense for which she originally received probation).
M.E. Hendrickson, Esq.
Alexandria, Virginia 22314
When your girlfriend was sentenced, did the judge impose and stay a sentence? If so, your girlfriend will do the time the judge imposed and stayed. If the judge withheld sentence and placed your girlfriend on probation, then there is likely a mechanism (such as "probation revocation") for bringing your girlfriend back before the same judge. Then, that judge will determine whether your girlfriend will do time related to the first offense.
While it is certainly more likely your girlfriend will do time now (either related to the new offense, or the first offense), a skilled attorney may still be able to assist her/keep her from going to jail. Perhaps, an attorney could help her find an alternative to jail (i.e., ani-shoplifting counseling/community service).
I strongly urge your girlfriend to consult with an attorney in your area who is experienced in these matters.
I am an attorney who represents clients regularly on probation violation matters in DC Superior Court. and although I do not represent you, I can explain the process generally for you. Technically, your girlfriend has violated her terms of probation by getting rearrested and a judge could already revoke her for a probation violation (despite her good record otherwise). It also does not help that the new rearrest charge is also a shoplifting charge. However, assuming what you say is true, in cases such as this, where a probationer is doing well except for the violation, what judges will sometimes consider is a process clled "trailing" a case. What happens is that the judge will not take any action until the new case is resolved. If it is resolved in her favor, then the judge may choose to not take any action revoking the probation, despite the arrest. If she is founds guilty or pleads guilty in the new case, then you will have to deal with repercussions in BOTH cases. Feel free to have your girlfriend contact me for a free consultation if you need some consultation. Regardless, good luck to you and your girlfriend!