I have not shoplifted. Growing up with family members who are law enforcement tends to put the fear of Dad in you.
Sorry to hear about your sister. If memory serves, shoplifting more than $1000 worth in AZ is a felony (class 6 being the lowest felony, on through class 1, which is the worst). I want to say a class 6 felony ? Not sure of the dollar amount, but I think after $2000, it's a class 5. If one has shoplifted in the past and was caught, depending on the amount, I think you get into class 5 to class 4 felony territory. That means she is facing between 1 to 3 years in prison, depending on which class of felony.
So based on what little info there is there, and considering it is Target, I would guess either your sister may have been caught in the past, or maybe she shoplifted something valuable, like jewelry.