Q:

GoogleScript - Google Sheets - Need to modify script to skip any lines of text that have matching variable

I have some code that I need help with. 
Right now when I run the script it fires regardless if the status is BLANK or set to SENT. I need to make sure the script does not run through SENT rows more than once.
I'm not an expert with Google Apps script and don't want to break the script's functionality.
function sendSms(to, body) {
  var messages_url = "https://api.twilio.com/2010-04-01/Accounts/MY_ID/Messages.json";

  var payload = {
    "To": to,
    "Body" : body,
    "From" : "+1PHONENUMBER"
  };

  var options = {
    "method" : "post",
    "payload" : payload
  };

  options.headers = { 
    "Authorization" : "Basic " + Utilities.base64Encode("MY_API:MY_API_TOKEN")
  };

  UrlFetchApp.fetch(messages_url, options);
}

function sendAll() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var startRow = 2; 
  var numRows = sheet.getLastRow() - 1; 
  var dataRange = sheet.getRange(startRow, 1, numRows, 2) 
  var data = dataRange.getValues();

  for (i in data) {
    var row = data[i];
    try {
      response_data = sendSms(row[0], row[1]);
      status = "sent";
    } catch(err) {
      Logger.log(err);
      status = "error";
    }
    sheet.getRange(startRow + Number(i), 3).setValue(status);
  }
}

function myFunction() {
  sendAll();
}

A:

You want to run sendSms() when the value of columns "C" is not sent.

If my understanding is correct, how about this modification? In this modification, the function of sendAll() was modified.
Modified script:
function sendAll() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var startRow = 2; 
  var numRows = sheet.getLastRow() - 1; 
  var dataRange = sheet.getRange(startRow, 1, numRows, 3); // Modified
  var data = dataRange.getValues();

  for (i in data) {
    var row = data[i];
    if (row[2].toLowerCase() != "sent") { // Added
      try {
        response_data = sendSms(row[0], row[1]);
        status = "sent";
      } catch(err) {
        Logger.log(err);
        status = "error";
      }
      sheet.getRange(startRow + Number(i), 3).setValue(status);
    }
  }
}

If this was not the result you want, I apologize. At that time, in order to correctly understand your situation, can you provide a sample Spreadsheet for replicating your situation? By this, I would like to modify the script.

