If "pathetic" was meant to describe someone who arouses pity and a sense of sadness, I think that Ismene represents this. I find it difficult to come down with intense criticism of Ismene because she is in a tragic predicament, if there ever was one. She is placed in between two equally desirable, but ultimately incompatible courses of action. On one hand, she has the Greek conception of woman. This conception is fairly direct in its assertion that women have little concern in the realm of politics and social policy. Their condition is one where they must respect the laws and abide by the social and political condition in which they live. If Ismene rejects this, she is cast out of Greek society, branded an outsider and treated as a pariah. This is the best case scenario for her.
On the other hand, there is loyalty for her sister. Nowhere in the play does she reject Antigone. She even volunteers to take the punishment for her. She remains loyal to Antigone, who pretty much severs connection to her when Ismene reflects to her that she is incapable of being able to fully embrace her plan. She has endured a great deal with her family. Tracing back to Oedipus, her brother/ father, and the suicide of her mother/ grandmother, as well as the death of her brother, and the refusal to honor him as per her uncle, Ismene has endured her share of familial pain and suffering. For Antigone to cut her off in such a brutal and swift manner is yet another familial relationship that has not provided emotional comfort for her. Ismene recognizes that her refusal to help Antigone will result in another severed bond.
How does one not feel pity for Ismene? The drama centers around Antigone, who ends up receiving some amount of redemption and absolution in Creon's admittance of error and the suffering that falls upon him. Yet, Ismene is discarded in terms of receiving any sort of resolution or hope for the future. She is left in a horrifically pathetic state at the end of drama, sister gone, and no familial connections of which to speak. She is not in a position of economic, social, or political power. She is literally silenced. I would entirely concede that she does not embody the bravery of Antigone. Yet, few do. In all honesty, one of the strongest elements that Sophocles displays is the stubbornness and difficulty that Antigone displays and causes to others. While she does stand for what is right, its cost is significant. For the freedom fighter, this is acceptable. Yet, for every freedom fighter are those who must remain behind and have to "clean up the mess" of idealism. They do not do so for praise and for glory. They do so out of love. Ismene is one of these individuals and for this, some level of pity is evoked, making her a pathetic character.