Yes Salad dressing can be your fat portion. If you're following the 1 - 2 - 3 method, then you need "a dash" of salad dressing, which means use sparingly and not drowning yourself in salad dressing!
Alternatively, I like to work things out, so I would check the label for the fat and workout how much you can have. E.g. Let's say the label looks like this one: http://www.calorie-count.com/calori.../4116.html
It shows 17% fat, or 11.1g of fat per 2 tbsp (31.0g). Now a fat block is 1.5g of fat, so 2 tbsp's is 11.1 / 1.5 = 7.4 blocks of fat, which is going to be too much for anyone.
Half that would be 3.7 blocks of fat from 1 tbsp, so depending on your meal size (let's assume you will be on a 3 blocker, like most women) then slightly under 1 tbsp will be right.
As a table spoon is about 3 tea spoons, you could (based on 17% fat salad dressing) say that 1 tea spoon, is roughly = 1 block of fat as a general rule.
And good luck Shauna!