I am of the opinion it was an excitement thing too! If she saw someone out of the window it may have been an "oh, look someone new" excitement
I remember when Archie was around four or five months he was sitting by the back door. My hands were soaked as I was washing up at the time so I went to dry my hands and Archie ran into the living room, jumped on the sofa and did a huge wee!!
I was so shocked as he was fully housetrained by then, like Sandy, and I couldn't understand why he did it!
Thankfully, it is a leather sofa and we have a throw over (for muddy paws) and it soaked into that, but that was the only time he "disgraced" himself.
Only problem we have with Archie is he jumps on the blanket box under our bedroom window and puts his front paws on the sill. Our window is always open and I am terrified in case he jumps out! Silly and it will never, ever happen, but as soon as he gets up there, I am behind him holding him
Getting back to Sandy though, she is ridiculously cute and could get away with anything and what a fab wake up call you get every morning! All I get is an Archie lying on my head
Kirsty and Archie