Anna had a tragic life, really.
A person has choices and she made a series of bad ones
A tragic life is someone in their late 20s with three young children and pregent with fourth while taking care of her 32 year old husband dying of cancer. Then continuing to work the remainder of her life up until she died of cancer age 65
I understand what you are saying, but the definition of a "tragedy" in the classic Greek theater was a story in which a fatal flaw in the protagonist's character brings him or her down. Anna Nicole Smith's life reflects that idea exactly.