As you say, unusual.
I wonder if she did actually see you or whether she ran on without really knowing what the threat was. When I bump munties in undergrowth I reckon, more often than not, that they have already seen me and just sit tight for a while before scarpering. Either that or they are totally oblivious to me until I'm nearly on top of them when both scent and sight will send them on their way. I have managed a few stalks on them where they seem to keep sniffing the air as if they are catching something they can't quite make out. There is a theory that prey animals can be highly inquisitive of novel sights and sounds if they aren't unduly alarmed. If she didn't see you and only caught a faint trace of your scent, her sense of a threat may have been insufficient to stifle her curiosity.
Interesting post, Pete. This is precisely what stalking is all about. Thanks.