how to deal with people feeding your lane

(i know i'm not perfect, and i would barely consider myself o'k. i'm silver 4, and most of my games i get 150 cs at 25 minutes)

if im playing darius top lane, and my lane opponent, fiora goes mid into a 2v1, to help out her team, who is outnumbered and behind, but my team jumps to her, and gets themselves killed, what can i do about that? i know i could follow her, but i didnt think i would need to. now im level 3, 1/0/0( i killed the jungler), and my lane opponent is 2/0/0, and level 5. what can i do at this point, other than try not to die? and if my jungler keeps coming, and dying, what can i do except sit there, get flamed by everyone in the game, when i only have 2 deaths? then we loose, because of fiora being extremely fed. i know i could have done a lot to help this not happen, but i dont know what these things are. if anyone could help me out, and tell me what i did wrong, and what i could have done to win, i would really appreciate it.

ps. i know i could have done a lot, like follow her early, and get her shut down early with my team, but i want to know more in depth tips.