I'm sorry to hear about this; I'm sure it must be hell for Haley and you at times. From my own experience, I would suspect that this is an issue concerning allergies and not parasites. I could be mistaken here, because parasites can be the cause of allergies as well.
I find it interesting that Haley would stop scratching after you used something else to clean the shower. That seems to indicate that she's very sensible to some stuff in her environment.
Dogs can also develop allergic behaviour when around certain plants on a regular basis. So, where do you live? In a city? The countryside? If countryside, is it farmland? Do you have cold, snowy winters, and if yes, is the scratching as bad then as in the warmer periods? Is your house heated and the air therefore dry? Are you keeping plants indoors? If yes, what kind of plants are they?
To determine what's happening here, there are a lot more questions that should be asked. Unless somebody can come up with an easy answer based on experience, the road ahead could be rocky. Just don't give up. Them good dogs deserve our concern and help.
You are surely on the safe side when trying to keep her as parasite-free as possible. If parasites could be excluded as a cause, then an important step has been done. And if parasites turn out to be the reason for her torment, then nobody complains once they have been killed. :-)
I hope RG can be a bit more specific than I have been and be therefore more helpful. But please keep us posted about any progress/regress happening. We can only learn from it. Well, at least we dog-keepers. :-)