Blanche is her own worst enemy. It is true that she had situations in life which left her to face desperate circumstances, to which she elected each of the outcomes.
When she found her husband in bed with another man, she pretended to shrug it off, and went out with BOTH that same night, as a way to mask her internal pain. Yet, she was no longer able to hold her contempt that same night, told her husband that he "disgusts her" and he went on and shot himself.
In this situation, Blanche was a victim, for this event follows her throughout the play, showing that it left her traumatized. However, no matter how we try to put the jigsaw of her life together, sleeping with her 17 year old student made no good case in her favor, no matter how love-starved she was.
When the family lost Belle Reeves, Blanche claims that she was the only one left to care for the plantation, and for her ailing family. Once list, she lived in a hotel in Laurel where, apparently, she did the same as as a prostitute: Sleep with men that would pay for her keep. She claims that these things led her to drink, and find some way to escape.
Finally, she shows up at her sister's house to literally disturb her peace, impose herself, and stay under a cloud of lies of what really happened. What was her purpose of her visit, but to escape her shady activity and try to land herself someone to take her on?
In this, she is no victim. She had choices, and she made all the wrong ones. Hers is not a case of victimization, but one of really bad common sense. Blanche tends to place herself in a position of self importance, then blame others for her misfortunes. However, she always had a chance to turn her life around. She had an education, talent, charm, and she knew how to get what she wanted. She may have a case of post traumatic stress due to the death of her husband, but she also had a clear path towards starting over. She chose not to.
Blanche has made some really bad choices, but I would say that her downfall started a log time ago. When she married her husband she apparently had no idea that he was gay. Once she found out she was horrified and wanted to expose him in her moment of upset. He killed himself.
Her husband's death set off a series of promiscuous relationships and as the years progressed alcoholism. Blanche had trouble managing finances and wanted to continue to live as a southern belle.
I believe that Blanche did have responsibility for her choices just based on the information that the reader is aware of. Stella made different choices and though her marriage may have some hints of abuse involved in many ways Stella is more stable than Blanche. She does not look to money for happiness.