Not the big issue, you can correct it when your file will come at visa office.
canadestin said:grave mistake......gawd .....declaring unmarried women as married ....
well cheer up.....nothing to worry......as long its the only mitsake (typo) ur cousin has done....i hope he/she dint send any document which shows he/she is married...like husbands name....kids etc.
she(sister) wont have any prob....its the applicants mistake...n yes he/she can rectify once the file reaches VO..remember not to delay.
BTW....y did u disappear?
Note: Mitali's suggestion will folow.....