Of is as you say....she was lucky and her victory was just a series of unfortunate circumstances for the other riders. I want to believe that there was no one that day that could beat her.
I also wouldn't call the rest of the peloton "unfortunate." They knew keeping track of the breakaway would be especially important given the lack of radio communication with a director in a team car, and they still didn't. I think Kiesenhofer deserves a ton of credit for this win; she was in the break from the very start of the race, and she was solo for over an hour, I believe. You can't do that without a lot of dedicated training and preparation. If anything, I think this is an example of "shoot your shot." You never know when things will break your way!
Part of the reason I love cycling races is that it's a combination of athletic ability and strategic thinking that you don't see in most other sports. The physics of drafting mean that a well coordinated group almost always has the speed advantage over a lone rider, but lone riders often win races because they don't have to deal with the coordination problems of a group. After 4+ hours of racing, people are trying to calculate optimal game theory decisions while at their max heart rate. It can be bonkers to watch!
This is why relative unknowns often break away. Especially as a professional. Nobody was watching Pedro Noname, but now the sponsors and recruiters know his name. Even if he doesn’t win, he’s gotten a good story and better prospects.
In this case it sounds like communication was bad and so if you didn’t see her break away then some people didn’t know she was gone. Or vastly underestimated her.
Big groups on a downhill are dangerous, on an uphill are too hot and cramped and so in both cases individual skill and power are outsized. If a technical downhill racer can break away on the last climb, they may be gone for the day. Tours have been lost or won on this tactic.
In a multi day tour a twelfth place competitor might pull away, even take a few people with them. The other teams may not be interested in catching, might have lesser members in the breakaway and be hedging their bets, so they can’t build consensus on burning their people to kick up the pace. They make think that they can wait for him to wear out and reel him in later, but there comes a point where from one update to the next they discover he’s still gaining on them, and oh shit do we still have time to catch? We better find out.
The worst for me is when they catch the breakaway mere miles from the finish line. Sometimes a person stays away all day only to end up finishing in the group, or at least beaten by all the sprinters.
Yeah, this is why I (and most others, I believe) find most of the sprint stages in the Tour pretty boring. The break vs. peloton dynamic is critical for road races to work (e.g. if there's no one up the road, why don't we all just ride along at 25kph?), but in those flat stages, the sprint teams are so good and care so much about the sprint finish that it's almost a guarantee they catch the break.