My sister had power of attorney. Is there a way I can see bank statements, what money was spent on, plus balance owed on her car?

If the person who assigned her has passed POA is no longer in effect. So, now we go to the Executor. If she is also Executor she has to probate the will and contact all beneficiares and interested persons. If you feel money has been spent unwisely, you have a right to an aldut. If you find the money was not used according to the POA, u can sue.

You say she "had" POA. What is the current status?