Oh, girl, I feel your pain! I had a dab (ok, I requested a DAB, I think it was closer to 2T!! But there were lots of veggies, I promise!) of ranch on a salad last week.
I don't think the problem is SO much about the fat itself, but more about the possible transfats and sugar.
So, if you look at the label and see transfat and sugar, you know the answer as to whether you "should" have eaten it!
As usual, I am not an expert. But my advice- toss out that ranch, check out Jen's recipes for Ranch, then forget about it. Put it behind you and just move on with Phase 1.