In the same vein she also (although generally stays within sight of us) won't come back to us when called, unless absolutely exhausted.
Have you tried hiding from her? I am known to dive behind trees/bushes etc. because Neo is very much a scent hound and this seems to make him deaf (although I don't generally think he's ignoring me, because he always looks surprised when he looks up to find me calling).
Never give chase either, walk in the opposite direction to Molly (hard I know). Have you also tried using a clicker? Start at home around the house, call her, and click and reward her when she comes and sits in front of you. Then do it in the garden and if you still don't trust her when out you can do it on a long line.. Thing is, is to start with small distances and build up, try it in different places, but obviously it will be alot harder on her usual off lead time. :roll:
I also use an arms open hand sign so that even if Neo can't hear me he knows I want him to come. I have also though about introducing a whistle. Once they reliable come for a treat, then start to only reward half the recalls, pick the best ones so they're never sure when they'll get rewarded, as cockers are great at working out patterns!
Ok I'm going to shut up now because I sound like a dog trainer and I'm not! Just something we've had to work on with Neo, cause he can get a bit lax in the old recall department!