I also wonder if they definitely saw her THAT day, she obviously walks Willow in the same area most days, could you really be 100% you definitely saw her in that location on Friday? and it wasn't Wednesday or Thursday?
I see my neighbour out with her little dog most mornings when I take my girls to school, but I couldn't be 100% certain where I saw her and on what days, sometimes it's down our lane, sometimes on the main road. If you asked me now, if i'd seen her last Friday, I definitely couldn't say with 100% certainty that i'd seen her on Friday or where, it all merges into one when you see someone in roughly the same area, most days.