<human>: Condense the text into a few key points

Backstory - My Dad left us (my mom and I) when I was a wee babe (I'm all good, my Mom is great) and later on had another daughter.  We did not grow up together - I was actually not aware of her existence until I was 21.  I've kept in touch with my Dad, mostly for her sake.  As such she reaches out to me mostly with how crappy my Dad is.  The majority of it is rants like this "its not fair" "he treats me like a kid" "he always compares me to you."  
Current issue at hand - my sister is in college (sophomore) and was recently caught stealing from a Wal*Mart with her friends. Why? Because she has stupid friends and she can be stupid too (aren't we all sometimes?)  Anywho, my Dad was all sorts of mad and essentially she is grounded for break and must stay at my Aunts place(stay at home mom).  I get a wall of text about this and how its unfair and how he's terrible and how she can't talk to him and how he treats her like a child, blah blah blah.  And I am completely at a lost of how to respond. From my adult side of things, she is a child, she is acting childish.  My Dad has every right to be mad and she needs to suck it up and deal with the consequences.  Everything that comes out of her mouth just sounds drama filled.  I'm having a hard time relating and giving good advice without sounding uncompassionate.  Also, I have no idea how to be "sisterly."  I grew up an only child, my strengths are not here.  So all those out there with younger siblings, how would you respond to this event?
<bot>: my sister got caught stealing my dad is pissed she is pissed (because he is pissed at her) and I don't know how to talk to her.