Arguing is pretty much an inevitable part of family life, because you've spent so long with a certain person and because ywe often don't feel the need to inhibit ourselves around our family members in the same way that we do with friends. From the fact that you are giving your sister advice it doesn't sound like she's having the easiest time at the moment so maybe this could be contributing to her behaviour and one her current situation improve she frequent arguments may stop. The fact that she's apologised to you suggests she doesn't wish to cause arguments but sometimes emotion/ frustrations get the better of us.
Especially the fact that she recieves less attention from your parents gives an understandable reason, but not a justification, as to why she may act in a certain way occasionally.
Does no one in your family ever argue? These arguments really do not sound severe enoiugh to warrant concern