This is an excellent and challenging question. I believe that Blanche is such a complex character that she is both the innocent and charming lady and the degenerate and promiscuous woman. She would like very much to be the woman she pretends to me, but that woman belongs to the past when she was young and was able to act the role of the Southern belle. She might be said to embody both the Old South and the New South in one confused and desperate character. She started to evolve into a different sort of woman as she grew older and her beauty faded along with her fortunes and expectations. She could easily be innocent and charming if she could find a man to provide for her and protect her. Perhaps the words "degenerate" and "promiscuous" are a little too strong. She is struggling to survive in a world in which she has little to offer except sexual appeal. Her interest in teenage boys may only show a desire to cling to her own youth. She was probably happiest when she was a teenager herself and had dozens of upper-class teenage boys infatuated with her. It is very hard to see her as a "bad" person. Stella understands her because they grew up together and shared their girlish dreams and secrets. Blanche's Southern belle persona may be artificial, but it was once sincere.
The character of Blanche duBois in A Streetcar named Desire is, if not necessarily a "likable" one, one with whom we can sympathize. The sympathy that the audience may feel for her comes from the extensive list of issues that she seems to have: she has experienced the pain of losing a home, of burying a husband to suicide, and of being deceived by such husband in a very cruel way.
However, she also has qualities that are less than redeeming. In her actions, we see clearly that every single choice that Blanche makes has been made with complete awareness and intention. For this reason, it is hard to suppose that Blanche is in ANY way innocent and charming. If anything, she is exacting, she does enjoy the pleasures of the libertine life, and she expects to fix her problems by landing herself in her sister's home, ruining her daily routine and marital life.
One of the moments in the play that shows Blanche's true persona is in Scene 5 when, right before a date with Mitch, she openly flirts and kisses a young adolescent boy who goes to collect the money for the newspaper. After kissing him and trying to seduce him, Blanche says, with no shame
“I've got to be good and keep my hands off children.”
This thought alone is quite troublesome. Already the audience knows that Blanche had lost her job as a teacher for having an affair with a young student. Now, she is making up to another young man again. If Blanche were a man trying to make up to young girls, wouldn't she be considered a form of pedophile? Moreover, does not Blanche reportedly have the capacity and ability to get any man that she wants by just using her charm? What business had she to do with young teenagers? What other inclination could she have to being with men, young and old alike, if not that she is the quintessential libertine?
Then there is her lying. She lies to Mitch by telling him that she is a virtuous, shy woman. She dims the light in his presence, and she acts the part of a prudish woman. With Stanley, she is flirtatious ad nauseating, thinking that, just by being a woman, she is safe from having her "dignity" harmed. She even lies to her sister about her shady past, which is why she was terrified when Stanley told her about meeting the man named "Shaw".
Hence, Blanche duBois is by no means innocent. Moreover, her actions point out that she is not charming, either. In fact, she is a nuisance to those around her; not having achieved anything, married anybody, or obtained a home anywhere--what is she but a middle-aged walking issue? It would be very hard to surpass the challenging complexities of Blanche's character. For this reason, it is hard to think of her as innocent or charming in any way.