After one week, Susy has 100+40 = <<100+40=140>>140 followers.
In the second week, Susy gains 40/2 = <<40/2=20>>20 new followers.
In the third week, Susy gains 20/2 = <<20/2=10>>10 new followers.
In total, Susy finishes the three weeks with 140+20+10 = <<140+20+10=170>>170 total followers.
After one week, Sarah has 50+90 = <<50+90=140>>140 followers.
After the second week, Sarah gains 90/3 = <<90/3=30>>30 followers.
After the third week, Sarah gains 30/3 = <<30/3=10>>10 followers.
So, Sarah finishes the three weeks with 140+30+10 = <<140+30+10=180>>180 total followers.
Thus, Sarah is the girl with the most total followers with a total of 180.
#### 180