Go with Giro. I have a narrowish foot (narrow end of B) and a narrower heel with a wider forefoot. My Specialized shoes are definitely too wide in the heel. We only just got Giro shoes, so I haven't tried them yet. The Scattantes were too wide in the heel even though they fit everywhere else, and same with LG. I tried men's Mavics (did you try Mavic?) and they were close, so the women's would be perfect for me. I haven't tried Sidi yet, but they last forever, so they may end up being cheaper in the long run. And if they fit well, then there's your answer.

The M520 is a mountain pedal, so you'll have to make sure that your shoe is either a mountain bike shoe (fit's generally close between lines, since I think they use the same last), or is drilled to accept 2- and 3-bolt cleats. I have M540s (a grade up; the 530 has the platform around it). Aside from being lighter, I don't think there's a ton of difference. I really like them, but my knees don't seem to. However, I have M545s on my cross bike and I think it's less the pedal and more a gearing problem.

I do recommend them (520s, since we don't carry the 540s) or the 530s to beginners because they're double-sided, so you don't have to hunt around to clip in. They're also fairly durable. The downside with the 540s is that I get hot spots around mile 30, but I think stiff shoes and a proper pedal stroke take care of that to some extent.