This is untested and based on your posting. Idk if you want it like that or not, but hope you can 'read' and understand the flow of script so you can expand from there.

on *:TEXT:followed:#:{
  ; if user say followed, fill var %last with value of $read(file.txt,1) 
  var %last $read(C:\Users\Blahh\Desktop\streamstuff\TwitchAlerts V0.56.9\Log\LastFollower.txt,1)
  ; check if var %previous.follower has value, fill it to %prev, otherwise %prev will be fill by %last value
  var %prev $iif(%previous.follower,$v1,%last)
  if %last != %prev { 
   ; %last != %prev, msg %last to channel, replace %previous.follower with %last     
    msg # %last
    set %previous.follower %last
  ; script done, waits for user say followed again.