Hmmm... yeah, I suppose to be honest there are a lot of fighting intricacies that one would have to take into account and I have a huge amount of respect for masters of the sport, which she undoubtedly is. To spend hours every day training in the art of fighting has to account for a lot. And smaller guys like Bruce Lee do come to mind in terms of kicking the head off some bigger guy.
I still do believe though that all else being equal, the bigger, stronger guy usually wins in a street fight. And I don't think its fair to say that Ronda would beat any guy who is not at her level of fighting expertise (a decent heavyweight, trained martial artist would have the upperhand surely).