How long has Maisie had an itchy problem? Has your vet done a York Test yet? Where is she the most itchy?
I have an itchy boy that I manage with a range of solutions, dependant on the severity and location. I have strategies for dealing with all sorts of issues which I can tell you about if you think it might help.
In the meantime have you used Piriton? Do check with your vet but it can be very effective for some dogs, calming the itch, scratch, itch cycle and giving time for other treatments to take effect.
Dermacton is another staple in my arsenal as is Ultrasalve from the same company. These are good products to use in conjunction with vet treatment and I find that Dermacton in particular is excellent at re moisturing the skin after the drying effects of Hibiscrub. Incidentally do make sure you use a very dilute solution of Hibiscrub - it's powerful stuff.
I also feed raw - I'm not sure yet how much difference it makes but I do feel better about giving him best chance to fight his allergies. You can get a lot of minces with the bone included whilst you pluck up courage for something more substantial.
Incidentally I think my boy was affected by our christmas tree. He had an obvious problem over christmas which stopped the day the tree got moved out. I suspect it wasn't a coincidence and I wish I'd twigged it sooner (pardon the pun!) :)