the kirigakure tried to kidnap rin to experement on rin and the put 3 tialed best name isubo on rin.. if rin and kakashi return to konoha the 3 tailed best will realise on her and will destroy the konoha.. and rin told kakashi to kill her cause she feels something inside her .. but obito is too late to save her.. thats my answers

the hidden kirigakuri ninja have kidnap rin to experiement on to put the 3 tailed best and rin notice it that something inside her and rin ask kakashi to kill her if rin goes to the konoha village the 3 tailed will realise on her and to destroy the konoha