Grey wagtail in Aberdeen

Hello. I'm not experienced in bird ID but I'm fairly sure I had a female grey wagtail in my garden in Aberdeen city centre for a few days last week. I was watching it because I liked its movements but didn't know how unusual it was for it to be here until I looked it up as I haven't been in Aberdeen so long myself. Apparently even its summer range doesn't extend this far north. From browsing books and online sources I can't see anything else that I could be confusing it with. Does anybody know of anything similar or is it not so unusual for a bird to be beyond its usual range in a mild year?