I gave my little sister a ride to a train station where she could catch a train the rest of the way home.
この場合、次のように言うのはどうでしょうか?
ーI gave my little sister a ride to a train station where she could catch a train the rest of the way home, so she wouldn't have to change trains.
「家までの残りの道のりを乗り換えなしで帰れるよう、妹を駅まで車で送ってあげた」
to give someone a ride to a train station で「人を駅まで車で送る・乗せてあげる」
to catch a train で「電車に乗る・間に合う」
rest of the way home で「家までの残りの道のり・道中」
to change trains で「電車を乗り換える」
ご参考まで!