Mate, I'm saying this with due respect ish. You've worked a dog, not a whippet, for four MONTHS, and you consider that is an appropriate amount of time for you to declare her to be a good working dog. Think about it mate, four months is a blink of an eye when it comes to working any dog. All lurchers, whippets etc, will take a couple of seasons really, before anyone could say 'they are a good worker.' What dog do have now, out of interest?
Your first couple of posts, and your replies since, have been a tad, how shall I put it? Sketchy, dicey, risky?
No malice intended mate, just m