Automatically Sending an Email based on a Google Sheet's cell value
Few minor things to improve:


you may unpack row in the for row in rows loop; moreover, you can use extended Python-3.x iterable unpacking  
use enumerate() to handle the indexing
remove unused pprint import
remove extra parenthesis around row[4] == "FALSE" and float(row[0])/30 &gt; 0.8 and send_email(is_sent, is_passing)
respect PEP8 guidelines - specifically, watch for spaces around the operators   
you can use an f-string to define the cell name


The code of the main() function with the above mentioned improvements applied:

for index, (score, *_, is_email_sent) in enumerate(rows):
    if is_email_sent != "FALSE":
        continue

    is_passing, is_sent = float(score) / 30 &gt; 0.8, False
    if send_email(is_sent, is_passing):
        worksheet.update_acell(f'E{index}', "TRUE")  # Updates the cell to reflect true
    else:
        print("these are not the droids you\'re looking for...")


I am, also, not really sure about that is_sent variable and send_email() having this argument. I think send_email should simply be responsible for sending an email and nothing - do one thing (Single Responsibility Principle). Printing out a message if an email was already sent should be done outside of the function.