Somehow I'm think TS want something more casual rather a fantasy or adventure title... Maybe something with comedy aspect and with teenage non/mild-romance relationship where they can laugh and chat together awhile watching it.
That why I'm recommend
Ookiku Furikabutte at my first recommendation, basically that are adaptation from baseball manga written by women author, so male-to-male relationship on this title is kinda interesting for a girl to watch it (don't worry its not a BL) and you will get fun together with your sister because the jokes is funny, the baseball game itself fascinating to watch, and maybe you two have a fun discussion about you and another-male relationship whether like shown in that anime too or not, or you can try
Hyakko (if your sister age is 12-or so)too, if you two enjoy
Minami-ke surely can enjoy this one too.
@scanner
why not
