Should I sympathize or keep my distance?

From the ages 3-10, my older sister was fine. Our mom had walked out on our family when I was two, but my dad was in the military, so we (little sister included) lived with our grandparents for 7 years. Then when I was 9, my dad got remarried and the first year, my sister was okay. In her 6-7 grades, she got into trouble with "friends". She ran away multiple times and even called the police on my dad once saying that he had "beaten her" (he didn't btw). She told all the shrinks that our step-mom was an evil b**** (she wasn't). I understand now that most was from her bipolar, but she continued with the behavior. Our parents got divorced last summer (bc of my sis) when we moved to MS. Heather just got into more trouble here with druggies so she went to boot camp for 5 months, but she came back. Recently, she stole our piano keyboard, PS2, 3 games, memory card, dvd player, tv, and other things. She's in jail now. She's threatened my family, and i've tried to make amends dozens of times.